feat(tools): add MiniMax voice cloning

[octo-patch]

Reason: Add executable voice cloning for the configured MiniMax backend.

Summary

• Add a voice_clone tool that uploads MP3, M4A, or WAV source audio and creates a reusable voice.
• Support global and China endpoints, optional prompt audio, transcript validation, normalization, noise reduction, preview text, and watermark controls.
• Inherit the configured MiniMax provider key and register the tool only when its media configuration is enabled.
• Parse upload and clone API status responses and return the created voice identifier.

Type

• Fix
• Feature
• Docs
• CI / tooling
• Refactor
• Other

Verification

• uv run --frozen pytest -q -p no:everos_plugin tests/test_media_gen_voice_clone_minimax.py (4 passed)

• uv run --frozen pytest -q -p no:everos_plugin tests/test_config_raven_sections.py (20 passed)

• uv run --frozen ruff format --check raven/agent/tools/media_gen.py raven/agent/loop/main.py raven/config/schema.py tests/test_media_gen_voice_clone_minimax.py

• uv run --frozen ruff check --ignore I001 raven/agent/tools/media_gen.py raven/agent/loop/main.py raven/config/schema.py tests/test_media_gen_voice_clone_minimax.py

• uv run --frozen python -m py_compile raven/agent/tools/media_gen.py raven/agent/loop/main.py raven/config/schema.py tests/test_media_gen_voice_clone_minimax.py

• git diff origin/main...HEAD --check

• Relevant tests pass locally

• Relevant lint / type checks pass locally

• User-facing docs or screenshots are updated when needed

Risk

• Security impact considered
• Backward compatibility considered
• Rollback path is clear for risky changes

The tool is opt-in and preserves existing media behavior. Rollback consists of removing the tool registration and its configuration field.

Related Issues

N/A