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.

OSGKeyboardShared/Models/LLMProvider.swift

@@ -82,6 +82,14 @@ public struct LLMProvider: Identifiable, Codable, Hashable, Sendable {
             apiKeyURL: URL(string: "https://platform.moonshot.cn/console/api-keys"),
             blurb: "Kimi · 长上下文 · Long context"
         ),
+        .init(
+            id: "mimo",
+            name: "小米 MiMo",
+            defaultBaseURL: "https://api.xiaomimimo.com/v1",
+            defaultModel: "mimo-v2.5",
+            apiKeyURL: URL(string: "https://platform.xiaomimimo.com"),
+            blurb: "mimo-v2.5 · 中文优化 · Chinese-optimized"
+        ),
         .init(
             id: "custom",
             name: "Custom · 自定义",