feat: implement auto-compaction CLI for intelligent data cleanup

This commit adds a comprehensive auto-compaction system for the Cortex CLI
backend with the following features:

Auto-Compaction Core (cortex-compact/src/auto_compaction.rs):
- CompactionLock: File-based advisory locking with stale lock detection
- atomic_write(): Atomic file operations using temp + rename + fsync pattern
- LogPruner: Age-based and size-based log cleanup with rotation
- DatabaseVacuumer: Session storage optimization and orphaned file cleanup
- AutoCompactionScheduler: Background thread-based scheduler with
  configurable intervals

CLI Commands (cortex-cli/src/compact_cmd.rs):
- 'compact run': Full compaction cycle
- 'compact logs': Log pruning only
- 'compact vacuum': Database vacuuming only
- 'compact status': Show compaction statistics
- 'compact config': Configure auto-compaction settings (placeholder)

Features:
- Race condition protection via file-system-safe operations
- JSON output support for automation
- Dry-run mode for safety
- Command aliases: gc, cleanup

All operations follow file system safety principles with atomic writes,
fsync for durability, and graceful error handling.

Author: factorydroid

Cargo.lock

@@ -37,6 +37,7 @@ cortex-update = { workspace = true }
 cortex-mcp-server = { workspace = true }
 cortex-share = { path = "../cortex-share" }
 cortex-snapshot = { workspace = true }
+cortex-compact = { path = "../cortex-compact" }
 
 clap = { workspace = true }
 clap_complete = { workspace = true }