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.

.gitignore

@@ -58,6 +58,9 @@ PreconfiguredKeys.local.swift
 # Lexicon build cache (downloaded SogouPopularDict TSV)
 .cache/
 
+# Custom LM compile output (Mac-only; device-side prepare uses .bin from bundle)
+OSGKeyboard/Resources/CustomLanguageModel/v1/compiled/
+
 # Python bytecode
 __pycache__/
 *.pyc