fix(web,ci): close TS↔Go type drift across 5 entities (D-2 master)

Closes five 2026-04-24 audit findings (all P2, all category cat-f /
diff-05x06-*) by reconciling the TypeScript interfaces in
web/src/api/types.ts with the on-wire JSON shape Go's
internal/domain/*.go structs actually emit. D-1 closed the same pattern
for one entity (Certificate / ManagedCertificate); D-2 covers the
remaining five.

Per-entity verdicts (audit's "stricter side is the contract"):

  Agent       — TRIM 5 phantoms (last_heartbeat, capabilities, tags,
                created_at, updated_at). Go emits last_heartbeat_at only.
  Target      — ADD 2 (retired_at?, retired_reason?) — I-004 fields.
  DiscCert    — ADD pem_data? — real field, real Go emit, omitempty.
  Issuer      — TRIM phantom status. Go has Enabled bool only.
  Notif       — TRIM phantom subject. Go has Message string only.
  Certificate — verify-only; D-1 closure confirmed clean at recon.

Consumer fixes (same commit as the trim):
- AgentDetailPage.tsx — remove dead Capabilities + Tags sections (always
  rendered empty); replace agent.created_at/updated_at row with the
  Go-emitted registered_at; widen heartbeatStatus() to accept undefined.
- AgentsPage.tsx — same heartbeatStatus widening.
- IssuersPage.tsx + IssuerDetailPage.tsx — issuerStatus() now derives
  from `enabled` exclusively; the dead `issuer.status || 'Unknown'`
  fallback is gone.
- NotificationsPage.tsx — drop dead `|| n.subject` fallback.
- NotificationsPage.test.tsx — drop dead `subject:` from mocks.
- api/utils.ts::timeAgo widened to accept string | undefined | null.
- api/types.test.ts — Agent (I-004) fixture trimmed of the 5 phantoms.

Tests (Vitest):
- 5 new describe blocks in web/src/api/types.test.ts:
  - Agent interface (D-2 phantom-fields trim) — 2 it blocks
  - Target interface (D-2 retirement fields) — 2 it blocks
  - DiscoveredCertificate interface (D-2 pem_data ADD) — 2 it blocks
  - Issuer interface (D-2 status phantom trim) — 1 it block
  - Notification interface (D-2 subject phantom trim) — 1 it block
- Each block uses the literal-construction pattern from D-1; trimmed
  fields are pinned via excess-property comments that compile-fail when
  uncommented if a phantom is reintroduced.

CI regression guardrail:
- .github/workflows/ci.yml — existing D-1 step renamed to "Forbidden
  StatusBadge dead-key + TS phantom-field regression guard (D-1 + D-2)".
  Three new awk-windowed greps over Agent / Issuer / Notification
  interfaces in types.ts. The Agent grep includes a `grep -v
  'last_heartbeat_at'` filter to avoid false positives on the
  legitimate Go-emitted heartbeat field.

Documentation:
- CHANGELOG.md — new D-2 section above B-1 under [unreleased] with full
  Added/Removed/Audit findings closed/Known follow-ups breakdown.
- docs/architecture.md — Web Dashboard section gains a new "TS ↔ Go
  type contract rule (D-1 + D-2 closure)" paragraph capturing the
  stricter-side-wins rule and the CI guardrail it's anchored by.
- coverage-gap-audit-2026-04-24-v5/unified-audit.md — Live Tracker score
  20/47 → 25/47 (P2: 6/27 → 11/27). Per-finding ✅ RESOLVED Status
  blocks added to all 5 diff-05x06-* entries plus the verify-only
  Certificate entry. Closed-bundle index gets D-2 row.

Verification (all gates green):
- cd web && tsc --noEmit                 → clean
- cd web && vitest run --reporter=dot    → 9 files, 302 tests passing
                                            (was 294 → +8 D-2 cases)
- cd web && vite build                   → clean
- go vet ./internal/... ./cmd/...        → clean (no Go touched)
- golangci-lint v2.11.4 run ./...        → 0 issues
- D-2 Agent guardrail dry-run            → empty (good)
- D-2 Issuer guardrail dry-run           → empty (good)
- D-2 Notification guardrail dry-run     → empty (good)
- D-2 Target ADD-shape sanity            → 2 retirement fields present
- D-2 DiscCert ADD-shape sanity          → pem_data present
- D-1 Certificate guardrail still clean  → empty (good)
- OpenAPI YAML parses                    → 89 paths

Audit findings closed:
- diff-05x06-7cdf4e78ae24 (P2, Agent TS↔Go drift)
- diff-05x06-2044a46f4dd0 (P2, Target TS↔DeploymentTarget Go drift)
- diff-05x06-85ab6b98a2f7 (P2, DiscoveredCertificate TS↔Go drift)
- diff-05x06-97fab8783a5c (P2, Issuer TS↔Go drift)
- diff-05x06-caba9eb3620e (P2, Notification TS↔NotificationEvent drift)
- diff-05x06-af18a8d7ef41 (P2) — verified clean since D-1; no edit

Deferred follow-ups:
- Issuer richer status view (enabled × test_status) — UX scope, not drift.
- Real Agent metadata (capabilities, tags) — backend feature, not drift.
- DiscoveredCertificate pem_data list-response perf — separate backend change.

docs/architecture.md

@@ -165,6 +165,8 @@ The dashboard includes an **ErrorBoundary component** for graceful error recover
 
 **Backend ↔ frontend round-trip rule (B-1 closure):** every backend CRUD operation must have at least one GUI consumer in `web/src/pages/`. Shipping a handler + repository method + OpenAPI operation + `client.ts` fetcher with no page that calls it leaves operators forced to `psql` directly — defeats the "every backend feature ships with its GUI surface" invariant and creates a destructive workflow when the missing path is `update*` (operators delete-and-recreate, losing FK history and audit-trail continuity). The CI guardrail in `.github/workflows/ci.yml` (`Forbidden orphan-CRUD client function regression guard (B-1)`) enforces this for the eight previously-orphan functions (`updateOwner`/`updateTeam`/`updateAgentGroup`/`updateIssuer`/`updateProfile` + `createRenewalPolicy`/`updateRenewalPolicy`/`deleteRenewalPolicy`); apply the same rule when adding any new write endpoint. If a fetcher is needed in `client.ts` before its consumer page exists, leave a TODO referencing this rule and ship them in the same commit.
 
+**TS ↔ Go type contract rule (D-1 + D-2 closure):** every TypeScript interface in `web/src/api/types.ts` must field-match the Go-side `internal/domain/*.go` struct's JSON-emitted shape exactly. Phantom fields (declared on TS, never emitted by Go) silently render `'—'` and lull consumers into thinking a value will arrive that never does; missing fields (emitted by Go, absent from TS) force `(x as any).X` escapes that lose type-checking. Both failure modes are blocked by the CI guardrail in `.github/workflows/ci.yml` (`Forbidden StatusBadge dead-key + TS phantom-field regression guard (D-1 + D-2)`) which awk-windows each interface and grep-fails the build on phantom-field reintroduction — currently covers Certificate (D-1), Agent / Issuer / Notification (D-2). Apply the same rule when adding any new on-wire type: the Go-side json tag is the contract, the TS interface adapts to it, and a literal-construction Vitest in `web/src/api/types.test.ts` pins the post-add shape. Stricter side wins: when in doubt, the side that actually emits the field is the contract; never propose adding a phantom on Go to match a TS over-declaration.
+
 ### PostgreSQL Database
 
 All state is stored in PostgreSQL 16. The schema uses TEXT primary keys (not UUIDs) with human-readable prefixed IDs like `mc-api-prod`, `t-platform`, `o-alice`.