refactor: relocate outbox I/O to session-manager + dead-code sweep

## Outbox extraction (delivery.ts → session-manager.ts)

File I/O for outbound attachments now lives in session-manager.ts alongside
the symmetric inbound extractAttachmentFiles. delivery.ts no longer touches
the filesystem — it hands buffers to the adapter and calls clearOutbox on
success.

- New `readOutboxFiles(agentGroupId, sessionId, messageId, filenames)` and
  `clearOutbox(agentGroupId, sessionId, messageId)` in session-manager.ts.
- deliverMessage in delivery.ts loses ~35 lines of fs/path code and its
  `fs`/`path` imports.

## Dead-code sweep

TypeScript's --noUnusedLocals surfaced several cruft imports. Fixed:

- src/container-runner.ts: drop unused `markContainerIdle` import; drop
  unused `session` parameter from `buildContainerArgs` signature.
- src/delivery.ts: drop unused `getSession`, `writeSessionMessage`,
  `wakeContainer` imports.
- src/host-sweep.ts: drop unused `updateSession`, `outboundDbPath` imports.
- container/agent-runner/src/poll-loop.ts: drop unused `config`,
  `processingIds` params from `processQuery`.
- Test files: drop unused imports in channel-registry.test, db-v2.test,
  host-core.test.

Skipped: `conversations` state in chat-sdk-bridge.ts (never read but
tangled with public `updateConversations` method; cleaning it risks a
merge conflict with the channels branch at the next sync).

## Validation

- `pnpm run build` clean
- `pnpm test` — 137 host tests pass
- `bun test` in container/agent-runner — 17 tests pass
- Service boots (`NanoClaw running`, `OneCLI approval handler started`)
  and shuts down cleanly on SIGTERM

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

container/agent-runner/src/poll-loop.ts

@@ -192,7 +192,7 @@ export async function runPollLoop(config: PollLoopConfig): Promise<void> {
     const skippedSet = new Set(skipped);
     const processingIds = ids.filter((id) => !commandIds.includes(id) && !skippedSet.has(id));
     try {
-      const result = await processQuery(query, routing, config, processingIds);
+      const result = await processQuery(query, routing);
       if (result.continuation && result.continuation !== continuation) {
         continuation = result.continuation;
         setStoredSessionId(continuation);
@@ -264,7 +264,7 @@ interface QueryResult {
   continuation?: string;
 }
 
-async function processQuery(query: AgentQuery, routing: RoutingContext, config: PollLoopConfig, processingIds: string[]): Promise<QueryResult> {
+async function processQuery(query: AgentQuery, routing: RoutingContext): Promise<QueryResult> {
   let queryContinuation: string | undefined;
   let done = false;
   let lastEventTime = Date.now();