perf(asr): speed up local Flow dictation and land CLM/keyboard refactor

Reduce perceived latency from key release to final text:
- Adaptive chunking: 2.5s first chunk + 5s follow-ups so short
  utterances start on-device recognition while still recording.
- Session-level ASR warmup and audio-format cache reuse to remove
  per-utterance cold-start of SpeechAnalyzer.
- Mirror live pipelined partials to the keyboard transcript line via
  a new flow.transcriptionPartial App Group key + Darwin ping.

Also commits the accumulated custom language model, Flow session,
keyboard extension restructure, and Xiaomi MiMo provider work in
progress on this branch.

OSGKeyboard/en.lproj/Localizable.strings

@@ -106,6 +106,7 @@
 "provider.qwen" = "Qwen (DashScope)";
 "provider.zhipu" = "Zhipu GLM";
 "provider.moonshot" = "Moonshot";
+"provider.mimo" = "Xiaomi MiMo";
 "provider.custom" = "Custom";
 "settings.api.title" = "API";
 "settings.language.title" = "Language";