fix: prevent mv lock timeout causing missing L0/L1 files

[r266-tech]

Closes #1047

Problem

The SemanticProcessor fails to move generated .abstract.md (L0) and .overview.md (L1) files from the temp directory to the target resource directory. Server logs show "Failed to acquire mv lock" errors, resulting in missing layer files even though the VLM successfully generated them.

Root cause: Two compounding issues:

1. TransactionConfig.lock_timeout and LockManager both default to 0.0, meaning any lock contention causes immediate failure — no waiting, no retry.
2. SemanticProcessor._sync_topdown_recursive() has no retry logic around viking_fs.mv() calls. When concurrent operations compete for subtree locks, the first contention kills the move.

Fix

1. Change default lock_timeout from 0.0 to 5.0 (seconds)

Updated in both TransactionConfig and LockManager/init_lock_manager. Five seconds is enough for transient contention to clear without causing indefinite blocking on real deadlocks. Users who want fail-fast behavior can still set lock_timeout=0.

2. Add retry logic with backoff for mv operations

New _mv_with_retry() helper in semantic_processor.py:

• Retries up to 3 times with increasing delay (0.3s → 0.6s → 0.9s)
• Only retries on lock-related errors (checks if "lock" is in the error message)
• Logs a warning on each retry for debugging
• Raises the original exception if retries are exhausted

Applied to all 4 viking_fs.mv() call sites in _sync_topdown_recursive().

Changes

File	Change
openviking_cli/utils/config/transaction_config.py	Default lock_timeout: 0.0 → 5.0
openviking/storage/transaction/lock_manager.py	Default lock_timeout: 0.0 → 5.0 (2 locations)
openviking/storage/queuefs/semantic_processor.py	New _mv_with_retry() helper, 4 call sites updated

3 files changed, +37/-13

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