fix(restore): add context validity checks to debug cancellation issues

Added explicit context checks at critical points:
1. After extraction completes - logs error if context was cancelled
2. Before database restore loop starts - catches premature cancellation

This helps diagnose issues where all database restores fail with
'context cancelled' even though extraction completed successfully.

The user reported this happening after 4h20m extraction - all 6 DBs
showed 'restore skipped (context cancelled)'. These checks will log
exactly when/where the context becomes invalid.

bin/README.md

@@ -4,8 +4,8 @@ This directory contains pre-compiled binaries for the DB Backup Tool across mult
 
 ## Build Information
 - **Version**: 3.42.50
-- **Build Time**: 2026-01-16_15:09:21_UTC
-- **Git Commit**: dd7c4da
+- **Build Time**: 2026-01-16_17:31:38_UTC
+- **Git Commit**: 698b8a7
 
 ## Recent Updates (v1.1.0)
 - ✅ Fixed TUI progress display with line-by-line output