Add VFS stat metadata command

[0xdewy]

Summary

• add bloom vfs stat <path> so agents can inspect VFS metadata without a privileged kernel mount
• expose modified_ms through daemon IPC lookup / list entry JSON
• print path, name, kind, mode, size, modified time, source, and symlink target when present
• add CLI coverage for in-process stat and daemon-routed stat preserving artifact timestamps

Stacking

• Stacked on [vfs] Surface natural metadata timestamps #97 (vfs_artifact_timestamps) because this command consumes the new Entry.modified metadata.
• Base branch: vfs_artifact_timestamps
• Implements Add non-mounted VFS stat or clearer mount permission UX #96. Because this PR targets a non-default stacked branch, GitHub will not auto-close Add non-mounted VFS stat or clearer mount permission UX #96 until this PR is retargeted/merged through master.

Verification

• cargo fmt
• cargo test -p bloom vfs_stat -- --nocapture
• cargo test -p bloom-daemon ipc --lib
• cargo check -p bloom
• git diff --check

Checklist

• Tests added or updated for behavior changes
• Architecture docs (docs/architecture/) updated if contracts or behavior changed — N/A: CLI metadata inspection command only
• Sealed Approval invariants respected (no signing outside a grant or bounded capability, no PRF/grant persistence, execution from sealed bytes) — N/A: read-only metadata lookup
• Agent Documentation updated (crates/bloom-vfs/src/docs/agent-guidance.md and affected Petal READMEs) — N/A: no VFS path semantics changed; command is discoverable via bloom vfs --help