Adds a Files section at the bottom of the server detail page that lists
the kernel-overlayfs merged view at runtime/<server_id>/merged/. Reuses
the overlay file-tree partial via two new template variables:
- files_base_url: parent passes "/overlays/<id>" or "/servers/<id>"
- download_supported: false for servers (runtime holds large game
binaries; no download endpoint), true for overlays (existing behavior)
New service helper safe_resolve_for_server_listing() rejects path
traversal beyond the merged root and returns None when the overlayfs
mount doesn't exist (server never started or just reset).
New route GET /servers/<id>/files?path=<rel> returns the lazy-load
file-tree fragment, gated to the server owner. No download counterpart.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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