Add sanitizeError() helper that strips file paths, stack traces, SQLite
errors, and system errors from messages before returning them to clients.
Applied to all route-level catch blocks in payments, queue, fights, and
admin routes. Includes 12 tests for the sanitizer and static analysis
test verifying no route files leak raw err.message.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>