feat: add configurable voice transcription

[LauraGPT]

Summary

• add opt-in voice transcription backed by any OpenAI-compatible /v1/audio/transcriptions endpoint
• configure the endpoint, model, and optional bearer token without bundling a speech runtime into NextChat
• proxy web requests through NextChat to avoid browser CORS failures; desktop builds call local endpoints directly
• append transcripts to the current draft without automatically sending the message
• release microphone tracks on success, recorder errors, construction failures, and component cleanup
• add English and Simplified Chinese settings copy plus recorder, request, config, and persistence coverage

The defaults target a local FunASR/SenseVoice-compatible endpoint at http://localhost:8000/v1, while remaining provider-agnostic. Web deployments use NextChat’s existing same-origin proxy boundary, so a colocated or network-reachable transcription service does not need browser CORS configuration.

Validation

• yarn test:ci --runInBand: 38 suites, 176 tests passed
• yarn tsc --noEmit: passed
• targeted ESLint for all changed files: 0 errors (4 existing warnings in chat.tsx)
• yarn build: passed

The full next lint command still hits the repository tooling crash in unchanged app/constant.ts:1 (unused-imports/no-unused-imports reading loc); the production build completes despite reporting that same lint-plugin warning.

Closes #6803

[LauraGPT]

Rebased onto current main (defdcdb5) and updated the implementation at signed+DCO head 4fd2ab76508367bba254b5dda307fe36f0538264.

The web path now uses NextChat’s same-origin proxy instead of requiring browser CORS from the transcription server; desktop builds continue to call local endpoints directly. Blank model values are rejected before upload, and the settings copy now follows the existing English/Simplified Chinese locale structure.

Exact-head validation:

• 38/38 Jest suites, 176/176 tests
• yarn tsc --noEmit
• targeted ESLint: 0 errors (4 existing warnings in unchanged portions of chat.tsx)
• production yarn build

The only full-lint limitation remains the repository tooling crash in unchanged app/constant.ts:1 (unused-imports/no-unused-imports reading loc); the build completes with that warning.

[codeCraft-Ritik]

Really solid work. I appreciate that the optimization focuses on eliminating unnecessary allocations while maintaining the same parser behavior. The additional regression tests around slicing, concatenation, and lazy evaluation make this a well-rounded change. 👏 @LauraGPT