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/server/src/server/agent/mcp-server.ts

@@ -14,7 +14,7 @@ import {
 } from "../messages.js";
 import { toAgentPayload } from "./agent-projections.js";
 import { curateAgentActivity } from "./activity-curator.js";
-import type { AgentSnapshotStore } from "./agent-snapshot-store.js";
+import type { AgentStorage } from "./agent-storage.js";
 import {
   appendTimelineItemIfAgentKnown,
   emitLiveTimelineItemIfAgentKnown,
@@ -47,7 +47,7 @@ import {
 
 export interface AgentMcpServerOptions {
   agentManager: AgentManager;
-  agentStorage: AgentSnapshotStore;
+  agentStorage: AgentStorage;
   terminalManager?: TerminalManager | null;
   getDaemonTcpPort?: () => number | null;
   scheduleService?: ScheduleService | null;