feat: add node update alerts with changelog tab and skip-version handling (#1463)

* feat: add node update alerts with changelog tab and skip-version handling

- Add node_update_available notification category with blue/brand bell dot
- Route node_update_available notifications to Fleet -> Node updates sheet
- Add Changelog tab to NodeUpdatesSheet with GitHub release notes
- Add per-node skip-version persistence (node_update_skips table)
- Skip hides update CTA on node card and sheet; re-surfaces on newer version
- Skipped nodes excluded from Update all backend filter
- Add pulsating dot indicator on Changelog tab when updates available
- Always-visible View changelog action in notification row bottom
- Admin-only for all mutating controls (skip, unskip, update)
- Backend tests for skip-version semantics (15 tests)
- Update fleet-view.mdx, remote-updates.mdx, and OpenAPI spec

* fix: address audit findings - nested button, stale changelog, semver normalization, mobile intent

- Move View changelog button outside routable button (sibling element)
- Fix aria-label for node_update_available notification rows
- Support ?recheck=true on release-notes endpoint
- Invalidate release notes cache on forced recheck
- Store normalized semver (semver.valid strips v prefix)
- Skip fleetUpdatesIntent on mobile (desktop only)
- Add v-prefix normalization test

* fix: restore View changelog on same line as timestamp, opposite sides

The button is always visible at the bottom right of the notification card,
on the same row as the timestamp (just now), using justify-between layout.

* fix: update tests for node_update_available category and release-notes fetch

- Backend: monitor-service tests now expect node_update_available instead of system
- Frontend: NodeUpdatesSheet tests mock release-notes API call to prevent undefined then()

* fix: resolve ci lint failures

docs/openapi.yaml

@@ -2372,11 +2372,96 @@ paths:
                           type: string
                           nullable: true
                           enum: [updating, completed, timeout, failed, null]
+                        skipActive:
+                          type: boolean
+                        skippedVersion:
+                          type: string
+                          nullable: true
         "401":
           $ref: "#/components/responses/Unauthorized"
         "403":
           $ref: "#/components/responses/Forbidden"
 
+  /api/fleet/nodes/{nodeId}/skip-version:
+    post:
+      operationId: skipNodeVersion
+      tags: [Fleet]
+      summary: Skip a node version
+      description: Marks a version as skipped for a node, hiding the update prompt and excluding it from update-all. Admin only.
+      parameters:
+        - name: nodeId
+          in: path
+          required: true
+          schema:
+            type: integer
+      requestBody:
+        required: true
+        content:
+          application/json:
+            schema:
+              type: object
+              required: [version]
+              properties:
+                version:
+                  type: string
+                  description: Semver version string to skip.
+      responses:
+        "204":
+          description: Skip recorded.
+        "400":
+          description: Invalid parameters.
+        "401":
+          $ref: "#/components/responses/Unauthorized"
+        "403":
+          $ref: "#/components/responses/Forbidden"
+        "404":
+          description: Node not found.
+    delete:
+      operationId: unskipNodeVersion
+      tags: [Fleet]
+      summary: Clear a node version skip
+      description: Removes the skipped-version record for a node. Admin only.
+      parameters:
+        - name: nodeId
+          in: path
+          required: true
+          schema:
+            type: integer
+      responses:
+        "204":
+          description: Skip cleared.
+        "400":
+          description: Invalid parameters.
+        "401":
+          $ref: "#/components/responses/Unauthorized"
+        "403":
+          $ref: "#/components/responses/Forbidden"
+        "404":
+          description: Node not found.
+
+  /api/fleet/update-status/release-notes:
+    get:
+      operationId: getFleetReleaseNotes
+      tags: [Fleet]
+      summary: Release notes for the latest Sencho version
+      description: Returns the GitHub release body and URL for the latest Sencho release, used by the Changelog tab.
+      responses:
+        "200":
+          description: Release notes.
+          content:
+            application/json:
+              schema:
+                type: object
+                properties:
+                  releaseNotes:
+                    type: string
+                    nullable: true
+                  htmlUrl:
+                    type: string
+                    nullable: true
+        "401":
+          $ref: "#/components/responses/Unauthorized"
+
   /api/fleet/nodes/{nodeId}/update:
     post:
       operationId: triggerNodeUpdate