fix(storage): detect and clear stale RocksDB LOCK files on Windows

[sliverp]

Problem

On Windows, when using OpenViking in local mode (SyncOpenViking with PersistStore), crashed or exited processes leave behind stale RocksDB LOCK files. All subsequent sessions fail with:

IO error: .../LOCK: The process cannot access the file because it is being used by another process

This is especially common with hook-based architectures (Claude Code hooks, MCP stdio servers) where many short-lived Python processes repeatedly open and close the same database. Even calling client.close() may not release the OS file handle until the Python process fully exits.

Root Cause

RocksDB creates a LOCK file when opening a database. On Windows:

1. Even after client.close(), the OS file handle may persist until process exit
2. If the process crashes/is killed/times out, LOCK is never released
3. Next process trying to open the same DB gets a PermissionError

Solution

Add _clear_stale_rocksdb_locks() in local_store.py, called before creating PersistStore. The function leverages Windows file semantics for an atomic staleness check:

• os.remove() succeeds → no process holds the file → stale lock → safe to remove
• os.remove() raises PermissionError → live process holds the file → leave it alone

On non-Windows platforms, the function is a no-op (Unix inode semantics mean the issue doesn't manifest).

Safety: RocksDB LOCK files are purely advisory (0-byte, contain no data). All actual data lives in SST files, WAL logs, and MANIFEST.

Tests

Added 5 tests in tests/storage/test_stale_rocksdb_lock.py:

• test_removes_stale_locks_on_windows — verifies cleanup on Windows
• test_skips_on_non_windows — verifies no-op on macOS/Linux
• test_handles_permission_error_gracefully — verifies live locks are kept
• test_handles_empty_directory — edge case
• test_handles_nonexistent_path — edge case

Closes #650
Ref #473, #576

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[zhoujh01]

#798

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Failed to generate code suggestions for PR

[zhoujh01]

Thanks for contributing the code. This fix is ​​similar to another previous code（https://github.com/volcengine/OpenViking/pull/798/changes ） fix, and I will have the person who wrote that code make the corresponding modifications based on this implementation. I'm closing this PR for now.