feat(server): add DCP clean-room context pruning

- Deduplication: removes consecutive identical tool_call+tool_result pairs
- Purge-errors: removes failed/empty tool results
- Transform orchestrator runs strategies in sequence pre-payload
- Wired into turn.ts before buildMessagesPayload
- Clean-room reimplementation (AGPL reference: behavior only)

apps/server/src/services/inference/dcp/index.ts

@@ -0,0 +1,4 @@
+export { transformMessages } from './transform.js';
+export type { DcpMessage } from './messages.js';
+export { toDcpMessages, fromDcpMessages } from './messages.js';
+export { getDcpState, clearDcpState } from './state.js';