feat(security): action-posture Security dashboard with exploit intel and triage (#1424)

* feat(security): reframe masthead as action posture, not worst-CVE severity

Derive the Security masthead from an action posture (Action needed /
Monitoring / Secure / Unknown) instead of raw scanner severity, and label
the raw Critical/High counts as scanner detections. "Secure" now means
nothing is actionable right now, never a claim that no vulnerabilities
exist; Unknown covers a missing scanner or a node with no completed scan.

Phase-1 bootstrap: "actionable" is approximated from the overview facts
that already exist (fixable findings, secrets, misconfigs); a later phase
moves the bucketing to the backend.

* feat(security): derive overview action posture from triaged facts

Add deriveSecurityPosture as the single bucketing function and extend
/security/overview with posture facts (fixableCriticalHigh, dangerousCompose,
accepted, rawCritical/rawHigh, plus knownExploited/publiclyExposed placeholders
that later phases populate) and the derived posture verb.

Suppression- and acknowledgement-aware counts come from one bounded read-time
pass over the latest-scan Critical/High findings, grouped per image so the
existing read-time filters apply unchanged. The pass is capped and flags
posturePartial, so a large node degrades gracefully instead of scanning every
detail row. The masthead now prefers the backend posture and keeps the local
bootstrap only as a fallback for older remote nodes reached through the proxy.

* feat(security): capture Trivy finding enrichment (status, CVSS, vendor, purl, layer)

parseTrivyOutput now keeps the per-finding fields Trivy already returns and we
previously discarded: Status (fixed / will_not_fix / end_of_life / ...), CVSS
(score + vector, preferring the NVD source then falling back), vendor severity,
package URL, package path, and layer digest. Persisted on vulnerability_details
via additive nullable columns (guarded ALTER), bound null when absent, and
carried through the cached-scan reconstruction path.

These fields separate scary from exploitable and feed the action posture and the
per-finding evidence tags. Field paths verified against Trivy's documented
image-scan JSON; covered by parse and insert/read round-trip tests.

* feat(security): add CVE exploit-intel service (CISA KEV + FIRST EPSS)

Add CveIntelService, a daily background cache of CISA KEV membership and FIRST
EPSS scores stored in a new cve_intel table and joined to findings at read time
by CVE id (never frozen onto scan rows, so a CVE entering KEV later lights up on
scans already stored). EPSS is fetched only for CVE ids present in stored
findings, batched; both feeds are best-effort and keep the last cache on
failure, so the Security page degrades gracefully offline. Wired into
startup/shutdown like the other background services.

The overview now counts known-exploited Critical/High findings, and KEV
membership escalates posture to Action needed even when no fix is available.

A per-instance "Exploit intelligence" toggle on the scanner setup surface lets
air-gapped or firewalled hosts disable the outbound fetch; the daily tick keeps
running but skips the fetch body when it is off.

* feat(security): show per-finding evidence tags (KEV, EPSS, vendor status, CVSS)

The vulnerabilities endpoint joins read-time exploit intel (KEV membership and
EPSS score) onto each finding by CVE id, and the scan sheet renders evidence
tags beside each CVE: known-exploited, EPSS probability, vendor will-not-fix /
end-of-life, and the CVSS score. Severity becomes one signal among several so an
operator can tell scary from exploitable, with no invented composite score.

* feat(security): evolve CVE suppressions into triage decisions

Layer a triage status and optional OpenVEX justification onto CVE suppressions.
Statuses: needs review / affected / not affected / accepted risk / fixed / false
positive / ignored. Dismissing states (not affected, accepted, fixed, false
positive, ignored) stop a finding from driving the action posture; needs review
and affected stay actionable and are surfaced as counts. Existing rows default
to "accepted" (the prior suppress behavior), so nothing changes for them.

The overview now reports needsReview / notAffected / accepted as distinct facts
derived from the triage status. The decision replicates across the fleet
(snapshot + replicated-insert carry status + justification) so a replica's
posture matches the control node. The inline suppress dialog gains a triage
decision selector; the read-time filter surfaces the status and justification on
every finding.

* feat(security): export fleet triage decisions as OpenVEX (Admiral)

Add an OpenVEX exporter that turns the instance's CVE triage decisions into a
standard VEX document (not_affected / fixed / affected / under_investigation,
with justifications), and a GET /security/vex/export endpoint to download it.
Authoring fleet VEX is a governance capability, so it is gated to Admiral (paid)
plus admin, mirroring the SARIF export gate; the Suppressions panel shows an
Export VEX action only on Admiral.

* docs(security): document action posture, evidence tags, exploit intel, and triage

Update the Security page and CVE suppressions docs for the action-posture
masthead (scanner detections vs product posture), per-finding evidence tags
(KEV / EPSS / CVSS / vendor status), the exploit-intelligence toggle (CISA KEV +
FIRST EPSS) on scanner setup, triage decisions layered on suppressions, and
OpenVEX export of fleet triage decisions.

* test(security): match intel hosts exactly in CveIntelService test

Route the fetch stub and its call assertions by exact hostname
(www.cisa.gov / api.first.org) instead of a domain substring check.
Resolves the js/incomplete-url-substring-sanitization code-scanning
alerts on the test's URL routing; behavior is unchanged.

backend/src/utils/suppression-filter.ts

@@ -12,10 +12,41 @@
  */
 import type { CveSuppression } from '../services/DatabaseService';
 
+/** Triage decision states layered on top of a suppression row. `accepted` is the
+ *  back-compat default for rows created before triage existed. */
+export const TRIAGE_STATUSES = [
+    'needs_review', 'affected', 'not_affected', 'accepted', 'fixed', 'false_positive', 'ignored',
+] as const;
+export type TriageStatus = typeof TRIAGE_STATUSES[number];
+
+/** Statuses that DISMISS a finding from the actionable posture (a decision was
+ *  made not to act). `needs_review` and `affected` are NOT dismissing: the
+ *  finding stays actionable and surfaces as a count. */
+export const DISMISSING_STATUSES: ReadonlySet<TriageStatus> = new Set([
+    'not_affected', 'accepted', 'fixed', 'false_positive', 'ignored',
+]);
+
+/** Optional OpenVEX-aligned justification taxonomy (never required). */
+export const TRIAGE_JUSTIFICATIONS = [
+    'vulnerable_code_not_in_execute_path', 'vulnerable_code_not_present',
+    'component_not_present', 'inline_mitigations_already_exist',
+] as const;
+export type TriageJustification = typeof TRIAGE_JUSTIFICATIONS[number];
+
+export function isTriageStatus(v: unknown): v is TriageStatus {
+    return typeof v === 'string' && (TRIAGE_STATUSES as readonly string[]).includes(v);
+}
+export function isTriageJustification(v: unknown): v is TriageJustification {
+    return typeof v === 'string' && (TRIAGE_JUSTIFICATIONS as readonly string[]).includes(v);
+}
+
 export interface SuppressionDecision {
+    /** True only when the matched decision DISMISSES the finding (see DISMISSING_STATUSES). */
     suppressed: boolean;
     suppression_id?: number;
     suppression_reason?: string;
+    triage_status?: TriageStatus;
+    triage_justification?: string | null;
 }
 
 export interface SuppressibleFinding {
@@ -113,11 +144,14 @@ export function applySuppressions<T extends SuppressibleFinding>(
         const bucket = buckets.get(f.vulnerability_id);
         const match = bucket ? pickFromBucket(bucket, f, imageRef, now) : null;
         if (!match) return { ...f, suppressed: false };
+        const status = (isTriageStatus(match.status) ? match.status : 'accepted');
         return {
             ...f,
-            suppressed: true,
+            suppressed: DISMISSING_STATUSES.has(status),
             suppression_id: match.id,
             suppression_reason: match.reason,
+            triage_status: status,
+            triage_justification: match.justification ?? null,
         };
     });
 }