refactor(v2): remove builder-agent dev-agent/worktree/swap flow

The dev-agent-in-worktree approach for source self-modification is abandoned
in favor of a direct draft/activate flow with OS-level RO enforcement
(planned, not yet implemented). Strip the whole subgraph:
src/builder-agent/, pending-swaps DB module + migration 006, builder-agent
MCP tools, and all host wiring (startup sweep, approval routing, deadman,
worktree mount, freeze gate). Tool descriptions in self-mod.ts / agents.ts
no longer cross-reference create_dev_agent. CLAUDE.md + v2-checklist updated
to describe the new direction.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/db/index.ts

@@ -65,18 +65,3 @@ export {
   updatePendingCredentialMessageId,
   deletePendingCredential,
 } from './credentials.js';
-export {
-  createPendingSwap,
-  getPendingSwap,
-  getInFlightSwapForGroup,
-  getSwapForDevAgent,
-  getAwaitingConfirmationSwaps,
-  getTerminalSwaps,
-  updatePendingSwapStatus,
-  setSwapPreSwapState,
-  startSwapDeadman,
-  extendSwapDeadman,
-  setSwapHandshakeState,
-  resetSwapForRetry,
-  deletePendingSwap,
-} from './pending-swaps.js';