feat(diag): host-side trigger-flow triage via 0xFD + mic_diag.sh bt-trace

Extends the firmware's 0xFD vendor feature report from 32 to 44 bytes
to carry the three host -> dongle -> BT trigger counters added in
5da1be4 (host_out02_total / host_out02_trig_allow / host_out02_to_bt).
mic_diag.sh's bt-trace decoder reads them and prints a one-line
verdict so the user can triage issue #3 in one terminal command
instead of switching to the OLED Diagnostics screen mid-game.

Verdicts encoded:
  host02 > 0, trig == 0       -> host driver never sets the trigger
                                 Allow bits; not a firmware problem.
  trig > 0, tx < trig         -> trigger Allow bits arrive but the
                                 speaker-active gate in main.cpp
                                 swallowed them.
  full chain populated        -> dongle delivered, controller didn't
                                 actuate; Sony BT-side limit.

The 0xFD report ID stays undeclared in the HID descriptor — Linux
hidraw ioctls don't enforce that and WebHID never sees these reports
(config goes through 0xF6). bt-trace's IOCTL_SIZE bumped to 45
(1 byte for the kernel-prepended report ID + 44 bytes payload).

Docs:
  README.md   - new "Diagnostics & debug tooling" section walks
                through the four mic_diag.sh subcommands; previously
                the script was only mentioned inside
                BLUETOOTH_AUDIO_NOTES.md.
  README.md   - Diagnostics-screen description updated for the
                scrolling row-list + cross-link to bt-trace.
  CLAUDE.md   - "Where features live" gets a host-side-diagnostics
                entry explaining how to extend the 0xFD payload and
                wire it into bt-trace's decoder.
  CHANGELOG   - records both the firmware extension and the README
                discoverability fix.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

README.md

@@ -186,6 +186,34 @@ Build flags worth knowing:
 - `-DENABLE_SERIAL=ON` — route printf to USB CDC for debugging (default OFF; releases UART for production builds).
 - `-DPICO_W_BUILD=ON` — build for the original Pico W (drops audio, lowers clock). Default targets Pico 2 W.
 
+## Diagnostics & debug tooling
+
+Two ways to triage bridge issues — on-device via the OLED Diagnostics screen, and host-side via `scripts/mic_diag.sh` (Linux). The host-side path is faster: no screen-switching, no flash cycle, runs while the controller is in active use.
+
+```
+# One-shot snapshot — is the dongle on USB? Did ALSA enumerate it? Is the
+# capture stream live? Is a controller currently paired?
+scripts/mic_diag.sh status
+
+# 3-second arecord on the mic IN endpoint — reports peak / RMS / non-zero
+# count so we can tell "stream is silent" from "stream is producing audio".
+scripts/mic_diag.sh capture 3
+
+# Same as `status` but in a loop, prints only on state change. Useful for
+# catching the exact second pairing completes or audio streams open / close.
+scripts/mic_diag.sh watch
+
+# Live read of the firmware's 0xFD vendor feature report (via /dev/hidraw):
+# BT input counts + rates, last seen non-0x31 IDs, byte prefixes, AND the
+# trigger-flow counters (host 0x02 received / with AllowTriggerFFB set /
+# forwarded to BT). bt-trace prints a verdict — "host driver isn't sending
+# trigger Allow bits" vs "forwarded but controller didn't actuate" — which
+# is what would otherwise need a USB protocol analyzer.
+scripts/mic_diag.sh bt-trace
+```
+
+Originally written to triage the parked DS5 BT-microphone investigation (see [BLUETOOTH_AUDIO_NOTES.md](./BLUETOOTH_AUDIO_NOTES.md)). The `0xFD` feature report and `bt-trace` decoder now also carry the trigger-flow counters added for [issue #3](https://github.com/MarcelineVPQ/DS5Dongle-OLED-Edition/issues/3) (missing adaptive trigger tension in some games).
+
 ## OLED Display Add-on (optional)
 
 If you plug a [Waveshare Pico-OLED-1.3](#hardware) onto the Pico2W's headers, the firmware drives it automatically as a live status display. No configuration needed — the firmware no-ops gracefully when no OLED is present.
@@ -249,7 +277,9 @@ Live render of the touchpad surface. Dots appear at current finger positions; th
 
 #### 7. Diagnostics
 
-Uptime, BT state, USB-audio frames/sec, BT 0x32 packets/sec, and HCI error counter — live values for verifying the audio path is moving bytes without needing a UART cable.
+Scrollable list of live counters — uptime, BT state, host → BT trigger flow (`host02` / `trig` / `tx`), BT 0x31 input rate, USB audio frames/sec, BT 0x32 packets/sec, and parked mic-investigation counters at the bottom. Controller D-pad ▲/▼ scrolls; tiny `^` / `v` glyphs at the right edge mark "more above/below." Read-only, so no cursor. Useful for verifying the bridge is moving bytes without needing a UART cable.
+
+The same counters are also exported on HID feature report `0xFD` for host-side tooling — see `scripts/mic_diag.sh bt-trace` below.
 
 <img src="./assets/oled/oled_sc07.jpg" alt="Diagnostics screen on the OLED" width="420">