Remove SQLite/Drizzle infrastructure from dev branch

Strip all database dependencies and revert to main's file-backed stores:
- Delete packages/server/src/server/db/ (schema, migrations, DB stores, legacy importers)
- Remove better-sqlite3, drizzle-orm, drizzle-kit, @electron/rebuild deps
- Revert bootstrap.ts to FileBackedProjectRegistry/WorkspaceRegistry/AgentStorage
- Restore workspace-registry-bootstrap.ts from main
- Revert AgentSnapshotStore → AgentStorage across all files
- Fix session.ts field names (directory→cwd, numeric id→string workspaceId)
- Remove DB-only tests from bootstrap.smoke.test, agent-manager.test, etc.

packages/desktop/package.json

@@ -5,10 +5,9 @@
   "description": "Paseo desktop app (Electron wrapper)",
   "main": "dist/main.js",
   "scripts": {
-    "build": "npm --prefix ../.. run build:daemon && npm run build:main && npm run rebuild-native && electron-builder --config electron-builder.yml",
+    "build": "npm --prefix ../.. run build:daemon && npm run build:main && electron-builder --config electron-builder.yml",
     "build:main": "tsc -p tsconfig.json",
     "dev": "./scripts/dev.sh",
-    "rebuild-native": "electron-rebuild -m ../.. -o better-sqlite3",
     "test": "vitest run",
     "typecheck": "tsc --noEmit -p tsconfig.json"
   },
@@ -20,7 +19,6 @@
     "ws": "^8.14.2"
   },
   "devDependencies": {
-    "@electron/rebuild": "^4.0.3",
     "@types/node": "24.6.0",
     "@types/ws": "^8.5.14",
     "electron": "41.0.3",