feat(updates): auto-apply and self-restart on new dashboard versions

Adds POST /api/updates/apply (pull, rebuild, restart) plus an "Update now"
button and hourly auto-check in the UI, for checkouts that are safely
fast-forwardable. Reintroduces self-restart (previously removed in edc25ca
for cross-environment reliability concerns) per explicit user request.

server/openapi.js

@@ -2440,6 +2440,48 @@ function createOpenApiSpec() {
           },
         },
       },
+      "/api/updates/apply": {
+        post: {
+          tags: ["Updates"],
+          summary: "Pull, rebuild, and restart the dashboard when fast-forwardable",
+          operationId: "applyUpdate",
+          responses: {
+            200: {
+              description:
+                "Checkout fast-forwarded and rebuilt; the process is about to self-restart",
+              content: {
+                "application/json": {
+                  schema: {
+                    type: "object",
+                    additionalProperties: true,
+                    description: "Same shape as GET /api/updates/status, plus applied: true.",
+                  },
+                },
+              },
+            },
+            409: {
+              description:
+                "Declined - nothing to apply, or the checkout isn't safely fast-forwardable",
+              content: {
+                "application/json": {
+                  schema: {
+                    type: "object",
+                    additionalProperties: true,
+                    description:
+                      'applied: false plus reason: "up_to_date" | "not_fast_forwardable".',
+                  },
+                },
+              },
+            },
+            500: {
+              description: "Update apply failed",
+              content: {
+                "application/json": { schema: { $ref: "#/components/schemas/ErrorResponse" } },
+              },
+            },
+          },
+        },
+      },
       "/api/alerts": {
         get: {
           tags: ["Alerts"],