fix(security): Apply 3 critical security fixes

- sec-001: Add validateAllowedPath to /api/file endpoint (path traversal)
- sec-002: Enable CSRF by default with CCW_DISABLE_CSRF opt-out
- sec-003: Add validateAllowedPath to /api/dialog/browse and /api/dialog/open-file (path traversal)

Ref: fix-1738072800000

Author: catlog22