Fix tail truncation, decouple call length from buffer, trim silence

Measured six recordings off a live P25 node and found two independent
defects causing lost audio at the end of calls:

- stop_recording() sliced the ring buffer immediately, so if the MP3
  muxer had not yet delivered the tail the file was silently short.
  Now waits (bounded, 2s) until buffered audio covers the end epoch.
- TGID-change closes used the new grant's epoch as the end with no pad
  at all, guaranteeing truncation on every split. Tail pad is now a
  setting, default raised 0.5s -> 1.0s.

The ring buffer also capped maximum call length: a call longer than the
buffer had its front silently clamped. The ring now serves the pre-roll
only, with a per-call accumulator for the rest, bounded at 4.8MB.
Clamping is loudly warned rather than silent.

Uploads averaged 63% silence, which inflates STT cost and is a known
Whisper hallucination trigger. Leading/trailing silence is now trimmed
conservatively (-40dB, 0.25s guard, internal pauses untouched).
started_at/ended_at still describe the call; new audio_* fields carry
the trimmed audio bounds so playback can map back to wall clock.
All-silence recordings are skipped and logged instead of uploaded.

Also: log measured control-channel idle on idle-timeout closes so
CALL_IDLE_TIMEOUT can be tuned from data, and quiet the httpx logger
which emitted ~170k lines/day of poll noise.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

drb-edge-node/app/internal/logger.py

@@ -7,4 +7,12 @@ logging.basicConfig(
     handlers=[logging.StreamHandler(sys.stdout)],
 )
 
+# The metadata watcher polls the OP25 terminal twice a second and httpx logs
+# every one of those requests at INFO ("HTTP Request: POST http://... 200 OK").
+# That is ~170k lines/day of pure noise which buries real events and makes field
+# log-reading useless. WARNING keeps genuine transport failures visible.
+# httpcore is the transport layer underneath httpx and is just as chatty.
+for _noisy in ("httpx", "httpcore"):
+    logging.getLogger(_noisy).setLevel(logging.WARNING)
+
 logger = logging.getLogger("drb-edge-node")