Fix Si4684 DAB response-parsing bugs found in firmware review

readDabServiceData(): 6 of 7 response fields (dataSrc, serviceId,
componentId, byteCount, segmentIndex, segmentCount) read one byte too
early, using the old raw[4]=RESP4 convention instead of the correct
raw[5]=RESP4 (established elsewhere in this driver by getPartInfo() and
readDabDigRadStatus()'s own ficQuality/cnrDb fields). dataSrc landing on
the wrong byte meant the DAB dynamic label (PAD/now-playing text) check
(dataSrc == 2) could essentially never match — it has likely never worked.
Header buffer grown 24->25 bytes to fit the correctly-positioned last field.

fetchDabServiceList(): didn't match AN649 Table 14's "DAB/DMB Digital
Service List" layout at all — serviceCount read from the wrong byte, every
per-service field misaligned, componentId assumed 4 bytes wide (actually
2 per the spec), and only the first of a service's possibly-several
components was ever skipped past (desyncing every later entry). Rewrote
against the actual Table 14 field layout. Confirmed live yesterday this
was producing garbled service_id/component_id/label output
(component_id values decoding as literal ASCII spaces).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0178rASQ6ZETPMUamvpoR2KR

Software/docs/si4684-rf-investigation-report.md

@@ -615,3 +615,20 @@ yet identified; unrelated to the Si4684 investigation (separate chip), but
 treat BT1035 boot failure as non-fatal rather than halting the whole device,
 so the rest of the system (Si4684 tuning, web UI, Wi-Fi) remains usable
 while this is investigated separately.
+
+## TODO (next session)
+
+- **Antenna/front-end calibration, now meaningful.** Before this session's
+  fixes, any ANTCAP sweep or front-end network experiment was untrustworthy
+  — a bad result could have been the software bug, not the antenna. Now
+  that the receiver chain is verified correct end to end (real FM lock,
+  real DAB lock, real audio), redo the ANTCAP sweep and compare the actual
+  front-end network (§ "Front-end network component mismatch" above)
+  against AN851 properly, with results that can actually be trusted.
+- Fix `fetchDabServiceList()` entry parsing (garbled service_id/component_id/
+  label) against AN649 §7 "Digital Services User's Guide" (~page 418).
+- Confirm actual DAB audio playback end to end (blocked on the item above).
+- Try a proper FM antenna to see if the residual noise under the music
+  clears up (suspected antenna quality, not yet confirmed).
+- BT1035 boot-failure root cause still open (see section above) — non-fatal
+  now, so it's no longer blocking, but still unexplained.