merge: tail-drain and chunked ASR hardening into main

Resolve FlowContinuousCapture by combining tail-drain gate/drain logic
with flow-abcd route-change and interruption recovery.

CHANGELOG.md

@@ -19,6 +19,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Changed
 - **Keyboard language label**: `PrimaryLanguage` set to `mis` so Settings no longer shows a misleading “English” subtitle under OSGKeyboard. / **键盘语言标签**：`PrimaryLanguage` 设为 `mis`，系统设置中 OSGKeyboard 下不再显示误导性的「英文」副标题。
 - **Flow ASR pipelining**: shorter first chunk (2.5s) and 5s follow-ups so short utterances start on-device recognition while still recording; session-level ASR warmup and format cache reuse; live partials mirrored to the keyboard transcript line. / **Flow ASR 流水线**：首块 2.5 秒、后续 5 秒，短句录音期间即开始端侧识别；会话级 ASR 预热与格式缓存复用；实时 partial 同步到键盘转写行。
+- **Flow tail drain**: after mic stop, capture drains trailing PCM (silence-detected, capped) before finishing the ASR stream; host finalize awaits drain; short final chunks re-transcribed with prior overlap; stitcher safe fallback when overlap merge would drop content. / **Flow 尾音排空**：停止录音后先排空尾部 PCM（静音检测 + 上限）再结束 ASR 流；主 App finalize 等待排空；过短末块与上一块 overlap 合并重识别；拼接误删时回退为安全合并。
 
 ## [0.4.0] - 2026-07-05