Add mount security allowlist for external directory access (#14)

* Add secure mount allowlist validation

Addresses arbitrary host mount vulnerability by validating additional
mounts against an external allowlist stored at ~/.config/nanoclaw/.
This location is never mounted into containers, making it tamper-proof.

Security measures:
- Allowlist cached in memory (edits require process restart)
- Real path resolution (blocks symlink and .. traversal attacks)
- Blocked patterns for sensitive paths (.ssh, .gnupg, .aws, etc.)
- Non-main groups forced to read-only when nonMainReadOnly is true
- Container path validation prevents /workspace/extra escape

https://claude.ai/code/session_01BPqdNy4EAHHJcdtZ27TXkh

* Add mount allowlist setup to /setup skill

Interactive walkthrough that asks users:
- Whether they want agents to access external directories
- Which directories to allow (with paths)
- Read-write vs read-only for each
- Whether non-main groups should be restricted to read-only

Creates ~/.config/nanoclaw/mount-allowlist.json based on answers.

https://claude.ai/code/session_01BPqdNy4EAHHJcdtZ27TXkh

---------

Co-authored-by: Claude <noreply@anthropic.com>

src/config.ts

@@ -6,6 +6,10 @@ export const SCHEDULER_POLL_INTERVAL = 60000;
 
 // Absolute paths needed for container mounts
 const PROJECT_ROOT = process.cwd();
+const HOME_DIR = process.env.HOME || '/Users/user';
+
+// Mount security: allowlist stored OUTSIDE project root, never mounted into containers
+export const MOUNT_ALLOWLIST_PATH = path.join(HOME_DIR, '.config', 'nanoclaw', 'mount-allowlist.json');
 export const STORE_DIR = path.resolve(PROJECT_ROOT, 'store');
 export const GROUPS_DIR = path.resolve(PROJECT_ROOT, 'groups');
 export const DATA_DIR = path.resolve(PROJECT_ROOT, 'data');