Add Parakeet MLX local speech support

[yaroslavyaroslav]

Summary

Adds local Parakeet MLX speech support to media understanding and registers the bundled hand configuration.

Changes

• Add Parakeet handling in media understanding runtime flow.
• Register the bundled clip hand updates needed for Parakeet support.
• Wire the hand registry so the new local speech path is available.

Testing

• cargo clippy --workspace --all-targets -- -D warnings passes
• cargo test --workspace passes
• Live integration tested (if applicable)

Security

• No new unsafe code
• No secrets or API keys in diff
• User input validated at boundaries

[jaberjaber23]

Incorporated Parakeet MLX support into main. Changed auto-detection to require explicit OPENFANG_ENABLE_PARAKEET_MLX env var (cloud providers like Groq should take priority by default, not be overridden just because uv is installed). Thanks.