Phase 12: file browser (0.12.0)

Add a full host filesystem browser reachable from the sidebar (/files):
breadcrumb navigation, browse-root chips, show-hidden toggle, and a table
with size/permissions/mtime. Text files open in a Monaco editor (language by
extension); binary/oversized files fall back to download. Admins can create
folders/files, rename, delete (recursive for dirs), upload, and save edits;
download is available to all users. Every mutation is audit-logged.

Backend: new services/file_service.py reuses device_service's sandbox helpers
(confined to ALLOWED_BROWSE_ROOTS, mapped via HOST_ROOT_PREFIX) and rejects
path traversal and deleting a browse root. routers/files.py exposes
/api/files/{list,read,download,write,mkdir,touch,rename,upload,DELETE}
(reads: any user; mutations: admin). device_service.browse entries gained
mtime + symlink (non-breaking).

Deployment: ALLOWED_BROWSE_ROOTS + HOST_ROOT_PREFIX are now env-wired in
docker-compose.yml and .env.example, with a commented /:/host_root mount to
browse/manage the real host filesystem.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docker-compose.yml

@@ -14,6 +14,11 @@ services:
       - NOTIFY_WEBHOOKS=${NOTIFY_WEBHOOKS:-}
       # Throwaway image used to snapshot named-volume contents during backups.
       - BACKUP_HELPER_IMAGE=${BACKUP_HELPER_IMAGE:-alpine:latest}
+      # File browser (sidebar) + volume host-path picker. ALLOWED_BROWSE_ROOTS
+      # limits which paths are reachable; HOST_ROOT_PREFIX is where the host
+      # filesystem is mounted inside this container (see the volume below).
+      - ALLOWED_BROWSE_ROOTS=${ALLOWED_BROWSE_ROOTS:-/,/mnt,/media,/srv,/opt}
+      - HOST_ROOT_PREFIX=${HOST_ROOT_PREFIX:-}
     volumes:
       - /var/run/docker.sock:/var/run/docker.sock
       - ./data:/data
@@ -22,6 +27,10 @@ services:
       # Host devices for GPU/device detection + passthrough (USB/TTY/DRI).
       # Read-only; remove if you don't need GPU/device features.
       - /dev:/dev:ro
+      # File browser: to browse/manage the real host filesystem, mount it here
+      # and set HOST_ROOT_PREFIX=/host_root in .env. Use :ro for read-only
+      # browsing, or drop :ro to allow edits/uploads/deletes from the UI.
+      # - /:/host_root
     expose:
       - "5008"
     # Uncomment to expose the API directly (normally proxied by the frontend):