chore(bins): retire unused migrate_exif

Single-library hardcoded (library_id=1) and missing content_hash/size_bytes
backfill, so the watcher's full-scan path subsumes everything it does.
Removed the binary and its CLAUDE.md reference.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

CLAUDE.md

@@ -69,9 +69,6 @@ cargo fix
 ```bash
 # Two-phase cleanup: resolve missing files and validate file types
 cargo run --bin cleanup_files -- --base-path /path/to/media --database-url ./database.db
-
-# Batch extract EXIF for existing files
-cargo run --bin migrate_exif
 ```
 
 ## Architecture Overview