chore: bump version to 0.4.0

New in 0.4.0:
- --version flag
- Security: random auth token, path-based cache delete, PRAGMA blocked
- CORS: POST methods, localhost origin, auth headers
- Safelist: fail closed on load error
- Accuracy tests for dir sizes and symlinks
- Remove dead code (query_dirs_by_name)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: bluedusk

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "diskcopilot"
-version = "0.3.0"
+version = "0.4.0"
 edition = "2021"
 description = "Fast, accurate Mac disk scanner and query tool"