Add auto-update system for DashCaddy instances

- self-updater.js: polls for new versions, downloads/verifies tarballs,
  triggers host-side rebuild via systemd path unit
- dashcaddy-update.sh + systemd units: host-side container rebuild with
  automatic rollback on health check failure
- 7 new /api/v1/system/* endpoints for version info, update check/apply,
  rollback, and update history
- Frontend: DashCaddy tab in Updates modal with version display,
  changelog, update button, rollback, and notification dot
- install.sh: updater service installation, volume mounts, env vars
- build-release.sh + webhook-handler.js: release server pipeline
  (Gitea webhook → build tarball → deploy to get.dashcaddy.net)
- Dockerfile: DASHCADDY_COMMIT build arg → VERSION file
- Version bump to 1.1.0

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

dashcaddy-api/routes/updates.js

@@ -59,5 +59,69 @@ module.exports = function(ctx) {
     res.json({ success: true, message: 'Update scheduled', scheduledTime });
   }, 'updates-schedule'));
 
+  // ===== DASHCADDY SELF-UPDATE ENDPOINTS =====
+
+  // Get current version
+  router.get('/system/version', ctx.asyncHandler(async (req, res) => {
+    const local = ctx.selfUpdater.getLocalVersion();
+    res.json({ success: true, name: 'DashCaddy', version: local.version, commit: local.commit });
+  }, 'system-version'));
+
+  // Check for DashCaddy update
+  router.get('/system/update-check', ctx.asyncHandler(async (req, res) => {
+    const result = await ctx.selfUpdater.checkForUpdate();
+    res.json({ success: true, ...result });
+  }, 'system-update-check'));
+
+  // Apply available update
+  router.post('/system/update-apply', ctx.asyncHandler(async (req, res) => {
+    const check = await ctx.selfUpdater.checkForUpdate();
+    if (!check.available) {
+      return res.json({ success: true, message: 'Already up to date' });
+    }
+    // Start async — container may restart
+    ctx.selfUpdater.applyUpdate(check.remote).catch(err => {
+      ctx.logError('self-update', err);
+    });
+    res.json({
+      success: true,
+      message: 'Update initiated',
+      fromVersion: check.local.version,
+      toVersion: check.remote.version,
+    });
+  }, 'system-update-apply'));
+
+  // Get update status
+  router.get('/system/update-status', ctx.asyncHandler(async (req, res) => {
+    res.json({
+      success: true,
+      status: ctx.selfUpdater.getStatus(),
+      lastCheck: ctx.selfUpdater.lastCheckTime,
+      lastResult: ctx.selfUpdater.lastCheckResult,
+    });
+  }, 'system-update-status'));
+
+  // Get self-update history
+  router.get('/system/update-history', ctx.asyncHandler(async (req, res) => {
+    const history = ctx.selfUpdater.getUpdateHistory();
+    res.json({ success: true, history });
+  }, 'system-update-history'));
+
+  // List rollback versions
+  router.get('/system/rollback-versions', ctx.asyncHandler(async (req, res) => {
+    const versions = ctx.selfUpdater.getAvailableRollbacks();
+    res.json({ success: true, versions });
+  }, 'system-rollback-versions'));
+
+  // Rollback to a previous version
+  router.post('/system/rollback', ctx.asyncHandler(async (req, res) => {
+    const { version } = req.body;
+    if (!version) return ctx.errorResponse(res, 400, 'version is required');
+    ctx.selfUpdater.rollbackToVersion(version).catch(err => {
+      ctx.logError('self-rollback', err);
+    });
+    res.json({ success: true, message: `Rollback to ${version} initiated` });
+  }, 'system-rollback'));
+
   return router;
 };