feat: unified fleet CLI, Main Chat preservation policy, sidechat routing, and file transfers

- Added CHAT_POLICY.md and README.md banner enforcing sidechat-first and file-transfer-first rules.
- Added strict Main Chat block to super dm send and super dm wo with --allow-main-chat override.
- Implemented file transfer staging and metadata registry in super dm send-file and super dm files (with clean subcommand).
- Added full job lifecycle management (show, create, enable, disable, delete, run --follow) to super-cli.py and box-ctl.py.
- Audited all jobs in jobs/*.json and redirected automated dispatches away from Main Chat.
- Hardened chromebox-watchdog.sh with systemd user session environment exports and stale singleton cleanup.
- Added compose_check command choice to muse-chat-api.py.

README.md

@@ -1,5 +1,10 @@
 # NetVM
 
+> [!IMPORTANT]
+> **CRITICAL POLICY: MAIN CHAT PRESERVATION**
+> Avoid using Main Chat whenever possible. When Main Chat gets bogged down with automated entries, scheduled job triggers, log dumps, or chatter, **work stops actually getting done**.
+> All inputs, scheduled jobs, health checks, and inter-agent coordination must be relayed via designated **sidechats** / **side agents**, or provided via **file transfers**. See [CHAT_POLICY.md](file:///home/super/Projects/NetVM/CHAT_POLICY.md) for full specifications.
+
 Fleet networking layer. Every node gets a stable network identity; every
 byte of automation traffic is attributable, consistent, and boring — the
 way good citizens look to the rest of the internet.