refactor: shared source — replace per-group agent-runner copies with single RO mount

Replace the per-group agent-runner-src copy model with a single shared
read-only mount. Source and skills are now RO + shared; personality,
config, working files, and Claude state stay RW + per-group.

Key changes:
- Mount container/agent-runner/src/ RO at /app/src (all groups share one copy)
- Mount container/skills/ RO at /app/skills; per-group skill selection via
  symlinks in .claude-shared/skills/ based on container.json "skills" field
- Mount container.json as nested RO bind on top of RW group dir
- Move all NANOCLAW_* env vars to container.json (runner reads at startup)
- New runner config.ts module replaces process.env reads
- Move command gate (filtered/admin) from container to host router
- Dockerfile: remove source COPY, split CLI installs (claude-code last),
  move agent-runner deps above CLIs for better layer caching
- Add writeOutboundDirect for router denial responses
- Design doc at docs/shared-src.md

Not included (follow-up): DB migration to drop agent_provider columns,
cleanup of orphaned agent-runner-src directories.

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

container/agent-runner/src/formatter.ts

@@ -55,6 +55,17 @@ export function categorizeMessage(msg: MessageInRow): CommandInfo {
   return { category: 'passthrough', command, text, senderId };
 }
 
+/**
+ * Narrow check for /clear — the only command the runner handles directly.
+ * All other command gating (filtered, admin) is done by the host router
+ * before messages reach the container.
+ */
+export function isClearCommand(msg: MessageInRow): boolean {
+  const content = parseContent(msg.content);
+  const text = (content.text || '').trim();
+  return text.toLowerCase().startsWith('/clear');
+}
+
 // eslint-disable-next-line @typescript-eslint/no-explicit-any
 function extractSenderId(msg: MessageInRow, content: any): string | null {
   const raw: string | null = content?.senderId || content?.author?.userId || null;