fix: Add input validation to prevent 'track not found' errors

Resolves issue where users got 404 errors by using generation taskId
as audio_id parameter. Added comprehensive validation that:

- Validates audio_id format (must be UUID)
- Validates task_id format (detects UUID in wrong param)
- Validates callback_url format (http/https only)
- Provides clear, helpful error messages
- Adds SSRF protection

Changes:
- suno_client.py: Added input validation with regex patterns
- test_wav_feature.py: Fixed test expectations for correct signature
- test_id_validation.py: NEW comprehensive validation test suite
- Removed redundant WAV_*.md documentation files

All tests passing. Ready for Docker rebuild and deployment.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: CodeKeanu