feat(dictate): add voice-reactive listening waveform

docs/adr/dictate/listening-level-events-26AUG2026.md

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+# Stream bounded audio levels for the dictate indicator
+
+Date: 26AUG2026
+Status: Accepted
+
+## Context
+
+Pi Dictate previously exposed only static service states. Active recording was easy to miss, and the extension had no signal from which to render a voice-reactive waveform. Raw microphone access must remain isolated in the host service.
+
+## Decision
+
+Protocol version 2 adds a `level` event while the service is listening. The recorder converts each 100 ms PCM window to a normalized logarithmic RMS level. The service sends the current scalar to the owning client at no more than 10 Hz.
+
+The extension renders a fixed-width footer status:
+
+```text
+● listening  ▁▂▄▇█▆▃▂▅▇▄▂
+```
+
+The circle uses Pi's semantic error color. Twelve block cells show recent levels as a scrolling history. Loading, stopping, and transcription remain static text.
+
+## Consequences
+
+- The indicator reacts to speech without granting Pi microphone access or sending PCM over the socket.
+- Output remains bounded by the existing per-connection queue and frame limits.
+- The extension and installed service must upgrade together because protocol version 1 clients do not understand level events.
+- Recording causes at most ten footer renders and protocol events per second.