feat(keyboard): improve typing, voice flow, and polish reliability

Reduce extension memory pressure and delivery races while adding richer candidates, tactile feedback, and safer two-level creative polishing.

docs/FLOW_BLUETOOTH_TESTING.md

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+# Flow Bluetooth HFP release gate
+
+Run this checklist on a physical iPhone before every release that changes Flow,
+PiP, ASR warmup, or audio-session code. Simulator audio is not an HFP substitute.
+
+## Required devices
+
+- Built-in iPhone microphone
+- One Bluetooth HFP headset (AirPods or equivalent)
+
+## Pass criteria
+
+1. Start a PiP Flow session and record 50 consecutive utterances with the
+   built-in microphone.
+2. Repeat 50 utterances with the Bluetooth headset already connected.
+3. Switch Prompt in the host app, return to the original text field, and record
+   20 more Bluetooth utterances.
+4. During recording, connect and disconnect the headset once. The app must
+   recover automatically before speech starts, or stop with an explicit
+   audio-device-changed error after speech has started.
+5. Recreate the keyboard extension once while processing and once after the
+   Host writes the final result.
+
+The run fails if any of the following occurs:
+
+- `-10868` or `formats don't match`
+- `capture.engine.startFailed`
+- A completed utterance reports zero input frames
+- `host.delivered` has no matching `keyboard.insert`
+- The same utterance is inserted more than once
+- A background task exceeds 30 seconds
+- AVAudioSession activation blocks the main thread
+
+Archive the filtered `[trace]` log with the release test record.