Add startup configuration banner, /config endpoint, and structured validation errors

[Copilot]

Makes API/CLI behavior predictable and self-documenting through explicit configuration logging, introspection endpoint, and improved error responses.

Changes

Startup Configuration Banner

• Lifespan handler logs environment on startup: mode, auth status, GCP project/region (when applicable), preset count
• UTF-8 logging, no secrets exposed

======================================================================
🎵 Music Track Generator API - Startup Configuration
======================================================================
Mode: gcp
API Key Authentication: yes
Google Cloud Project: my-project
Google Cloud Region: us-west1
Available Presets: 5 loaded
======================================================================

/config Endpoint

• Returns safe runtime configuration: mode, region, project, available presets, auth status
• Respects authentication when configured

{
  "mode": "gcp",
  "region": "us-west1",
  "project": "my-project",
  "presets_available": ["rock_anthem", "jazz_smooth", ...],
  "auth_enabled": true
}

Structured Validation Errors

• Custom RequestValidationError handler returns 422 with field-level details
• Clear field identification for debugging

{
  "detail": "Validation error",
  "errors": [
    {
      "field": "body.duration_seconds",
      "message": "Input should be greater than or equal to 60",
      "type": "greater_than_equal"
    }
  ]
}

Makefile

• Common targets: venv, install, test, api, cli-help, clean

Documentation

• README updated with expected outputs for simulate mode
• /config endpoint documented with examples

Original prompt

Goal

Make the API/CLI behavior predictable and self-documenting, especially around environment configuration, without changing core features.

Tasks

1. Startup Log Banner in src/music_generator/api.py:
   • Add a startup event handler that prints a banner with:
     • MUSIC_GEN_MODE value.
     • Whether MUSIC_GEN_API_KEY is set (yes/no).
     • GOOGLE_CLOUD_PROJECT and GOOGLE_CLOUD_REGION when in gcp mode.
2. New /config Endpoint:
   • Add a GET /config endpoint in api.py that returns safe configuration info:
     • mode, region, project (if any), presets_available, auth_enabled (true/false).
     • Ensure no secrets are returned.
3. Improved Error Handling:
   • In generate_track (/tracks/generate), ensure duration_seconds is validated.
   • Return a structured 422 error with field names for validation failures.
   • Use a custom exception handler for RequestValidationError to format errors.
4. Add a Makefile:
   • Include targets: venv, install, test, api, cli-help.
5. Update README.md:
   • Add exact commands and expected outputs for simulate mode.
6. Update Tests:
   • Update tests/test_api.py to include tests for the new /config endpoint and structured error responses.

Constraints

• Keep current endpoints stable.
• Do not implement a real Vertex AI music model call yet.
• No silent fallbacks: print clear logs for mode/auth/config at startup.
• UTF-8 logs and no secrets in logs.

This pull request was created from Copilot chat.

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