feat(fleet): add remote node update management (#353)

Add the ability to check for outdated nodes and trigger over-the-air
updates from Fleet View. Nodes self-update by pulling the latest Docker
image and recreating their container via the "last breath" pattern.

Backend:
- SelfUpdateService: self-container identification via HOSTNAME + Docker
  Compose labels, triggers pull + force-recreate
- CapabilityRegistry: runtime capability disabling via disableCapability()
- POST /api/system/update (202 + deferred self-update)
- GET /api/fleet/update-status (version comparison across fleet)
- POST /api/fleet/nodes/:nodeId/update (single node)
- POST /api/fleet/update-all (bulk remote update)
- In-memory update tracker with 5-min timeout

Frontend:
- Node Updates modal with summary stats, search filter, table layout,
  per-node Update buttons, and bulk Update All
- Version badges and update-available indicators on node cards
- ReconnectingOverlay for local node updates (polls /api/health)
- 5s fast-poll when any node is actively updating
- UpdateStatusBadge shared component for consistent badge rendering

Requires Skipper (Pro) tier. Nodes must be deployed via Docker Compose
with Docker socket access.

docs/docs.json

@@ -104,6 +104,7 @@
               "features/multi-node",
               "features/node-compatibility",
               "features/fleet-view",
+              "features/remote-updates",
               "features/stack-labels",
               "features/alerts-notifications",
               "features/notification-routing",
@@ -149,7 +150,8 @@
             "group": "Health & Meta",
             "pages": [
               "GET /api/health",
-              "GET /api/meta"
+              "GET /api/meta",
+              "POST /api/system/update"
             ]
           },
           {
@@ -222,6 +224,9 @@
               "GET /api/fleet/overview",
               "GET /api/fleet/node/{nodeId}/stacks",
               "GET /api/fleet/node/{nodeId}/stacks/{stackName}/containers",
+              "GET /api/fleet/update-status",
+              "POST /api/fleet/nodes/{nodeId}/update",
+              "POST /api/fleet/update-all",
               "POST /api/fleet/snapshots",
               "GET /api/fleet/snapshots",
               "GET /api/fleet/snapshots/{id}",