Persist harness projects to database

Projects were stored purely in useState — lost on every page refresh.
- Add harness_projects table (id, name, workspaces jsonb)
- Add /api/projects CRUD route (GET/POST/PUT/DELETE)
- Load projects from DB on dashboard mount
- All project mutations (create, delete, add/remove repo) now
  persist via API calls

packages/db/drizzle/meta/_journal.json

@@ -15,6 +15,13 @@
       "when": 1774127485727,
       "tag": "0001_stale_pride",
       "breakpoints": true
+    },
+    {
+      "idx": 2,
+      "version": "7",
+      "when": 1774178806032,
+      "tag": "0002_cold_annihilus",
+      "breakpoints": true
     }
   ]
 }