feat: open security basics, manual fleet ops, and basic fleet management to Community (#930)

Realign tier guards to the user-stated philosophy: Community covers
deploy/monitor at scale plus security basics, Skipper adds automation
and advanced fleet management, Admiral keeps enterprise control.

Community now includes:
- Trivy install / uninstall / update from the Settings Hub (admin role)
- CVE suppressions CRUD (admin role; replicates fleet-wide)
- Manual image scan with vuln, secret, and misconfig results
- Stack-config scan, scan comparison
- Manual fleet snapshots: create, list, view, restore, delete
- Per-node Sencho self-update (Check Updates + per-node Update)
- Fleet Overview search, sort, filters, node-card expand, auto-refresh

Stays paid:
- Scan policies with block_on_deploy enforcement (Skipper+)
- SBOM (SPDX, CycloneDX), SARIF export (Skipper+)
- Bulk Update All across the fleet (Skipper+)
- Scheduled snapshot create (now Skipper, was Admiral)
- Trivy auto-update toggle, fleet-wide policy push (Admiral)

The Settings -> Security tab is unhidden by setting the registry tier to
null. The SecuritySection no longer early-returns a PaidGate; the policy
list, Add Policy button, and policy dialogs are wrapped in {isPaid && }.
The Fleet view drops isPaid gates on the Snapshots tab, Check Updates
button, per-node update handlers, OverviewToolbar grid controls, the
NodeCard expand affordance, and the auto-refresh notice. The
NodeUpdatesSheet receives a canBulkUpdate prop and gates the Update All
button on it. useFleetUpdateStatus and useFleetPolling drop their isPaid
guards so polling runs for Community; useFleetOverview drops the isPaid
wrap on the filter and sort path.

Backend route guards are flipped per the matrix above. The scheduler
tick and requireScheduledTaskTier add 'snapshot' to the Skipper+ branch.
Backend test assertions are inverted for the now-Community endpoints
and a positive Skipper-snapshot-task test is added.

Documentation across features/, api-reference/, and operations/ is
updated to reflect the new tier mapping.

docs/api-reference/security.mdx

@@ -5,7 +5,7 @@ description: Automate scan policies, CVE suppressions, and vulnerability scans f
 
 The Security API lets you manage scan policies, CVE suppressions, and trigger vulnerability scans from CI pipelines and automation scripts. Every endpoint in this reference is intended for external automation; internal frontend-only endpoints (finding listings, SARIF downloads) are not documented here.
 
-All endpoints require [Bearer token authentication](/api-reference/overview#authentication) and most are gated to Skipper or Admiral. See the per-endpoint **License** row for details.
+All endpoints require [Bearer token authentication](/api-reference/overview#authentication). Manual scans, secret and misconfiguration results, scan comparison, and CVE suppressions are available on every tier. Scan policies (with `block_on_deploy` enforcement), SBOM, and SARIF stay on Skipper or Admiral. See the per-endpoint **License** row for details.
 
 ## Scan policies
 
@@ -120,7 +120,7 @@ Suppressions let you mark individual CVEs as acknowledged so scan reads, compari
 
 **`GET /api/security/suppressions`**
 
-**License:** Skipper or Admiral
+**License:** Community
 
 Response rows include an `active` boolean computed from the `expires_at` timestamp.
 
@@ -145,7 +145,7 @@ Response rows include an `active` boolean computed from the `expires_at` timesta
 
 **`POST /api/security/suppressions`**
 
-**License:** Skipper or Admiral · **Role:** Admin
+**License:** Community · **Role:** Admin
 
 | Field | Type | Required | Description |
 |-------|------|:--------:|-------------|
@@ -176,7 +176,7 @@ curl -X POST https://your-sencho-instance:1852/api/security/suppressions \
 
 **`DELETE /api/security/suppressions/{id}`**
 
-**License:** Skipper or Admiral · **Role:** Admin
+**License:** Community · **Role:** Admin
 
 ```bash
 curl -X DELETE https://your-sencho-instance:1852/api/security/suppressions/3 \
@@ -189,7 +189,7 @@ curl -X DELETE https://your-sencho-instance:1852/api/security/suppressions/3 \
 
 **`POST /api/security/scan`**
 
-**License:** Community for vulnerability-only scans. Skipper or Admiral when `scanners` includes `secret`. · **Role:** Admin
+**License:** Community · **Role:** Admin
 
 Accepts an image reference and starts an asynchronous scan. The response returns immediately with a `scanId` that you can poll.
 
@@ -198,7 +198,7 @@ Accepts an image reference and starts an asynchronous scan. The response returns
 | `imageRef` | string | yes | Image reference Trivy will scan (must match Sencho's validator; `/`, `:`, `@`, alphanumerics, `-`, `_`, `.`). |
 | `stackName` | string | no | Associates the scan with a stack for display purposes. |
 | `force` | boolean | no | Default `false`. When `true`, ignores the 24-hour digest cache and runs Trivy again. |
-| `scanners` | `["vuln"]` or `["vuln","secret"]` | no | Omit for vuln-only. `secret` requires Skipper or Admiral. |
+| `scanners` | `["vuln"]` or `["vuln","secret"]` | no | Omit for vuln-only. Pass `["vuln","secret"]` to include secret detection. |
 
 ```bash
 curl -X POST https://your-sencho-instance:1852/api/security/scan \