Add cascade delete for projects with Gitea repository cleanup

- Add deleteGiteaRepo server action to remove repos via Gitea API
- Add deleteProject function with full cascade:
  - Deletes Gitea repository if linked
  - Removes all agent_runs, messages, backlog items
  - Removes project phases, activities, recommendations
  - Finally removes the project itself
- Add ProjectSettingsMenu with delete confirmation dialog
- Add use-toast hook for notifications using sonner
- Add shadcn alert-dialog component
- Restore brand button variant after shadcn update

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

package.json

@@ -9,6 +9,7 @@
     "lint": "eslint"
   },
   "dependencies": {
+    "@radix-ui/react-alert-dialog": "^1.1.15",
     "@radix-ui/react-avatar": "^1.1.11",
     "@radix-ui/react-dialog": "^1.1.15",
     "@radix-ui/react-dropdown-menu": "^2.1.16",