chore: normalize line endings (CRLF -> LF)

No content changes: git diff --ignore-all-space over these files is empty.
The churn came from editing on Windows against a repo checked out with LF.

backend/db/migrations/002_add_file_hash.sql

@@ -1,4 +1,4 @@
--- Migration: 002_add_file_hash
--- Description: Add file_hash column to documents table for duplicate content detection
-
-ALTER TABLE documents ADD COLUMN IF NOT EXISTS file_hash VARCHAR(64);
+-- Migration: 002_add_file_hash
+-- Description: Add file_hash column to documents table for duplicate content detection
+
+ALTER TABLE documents ADD COLUMN IF NOT EXISTS file_hash VARCHAR(64);