Add --watch/--ford/--pid/--scan modes + 2026-06-29 session diagnostics

obd_reader.py:
- Mode 22 plumbing: ELM.mode22() sends a 16-bit PID request, parses both
  positive (62 ..) and negative (7F 22 NRC) responses.
- --ford runs a small TENTATIVE table of community-sourced Ford 6.0 PIDs
  (ICP/IPR/FICM/EBP/EOT). All printed with raw bytes for verification.
- --pid XXXX probes a single PID and prints multiple candidate decodings
  (u8, u16, mV, temp, duty) so we can eyeball the right scaling.
- --watch [N] streams ATRV + module voltage (PID 0142) for N seconds.
  Designed for capturing voltage sag during cranking.
- --scan AAAA-BBBB brute-force scans Mode-22 PIDs with --scan-log PATH
  for output. Uses fast ELM timing (ATAT2, ATST19) for ~3.5 PIDs/sec.

diagnostics/2026-06-29-no-start/:
- Captured cranking voltage trace, full Mode-22 scan (1000-14FF -> 46
  hits), and a session writeup. Working hypothesis: not batteries, not
  fuel -- ICP / FICM / CMP. FICM meter test still owed.

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

diagnostics/2026-06-29-no-start/mode22-scan-hits.txt

@@ -0,0 +1,48 @@
+# Mode-22 scan 1000-14FF
+# pid_hex  len  raw_bytes
+1100  7  01 00 40 05 7F 22 12
+1101  5  00 62 11 01 00
+1102  1  00
+1103  5  00 62 11 03 00
+1104  5  00 62 11 04 00
+1105  1  00
+1106  5  00 62 11 06 04
+1107  5  00 62 11 07 00
+110C  4  00 7F 22 12
+1123  5  1E 62 11 23 30
+1125  1  FF
+1126  5  00 62 11 26 00
+1127  1  E7
+1135  2  FF FF
+1139  5  2E 62 11 39 2E
+114A  5  7E 00 7F 22 12
+114B  5  A6 56 7F 22 12
+114D  2  81 40
+1155  2  FF FF
+1165  7  00 00 62 11 65 00 00
+1169  2  00 00
+1172  5  D1 62 11 72 D3
+1177  5  00 C8 7F 22 12
+11B3  1  02
+11B4  2  00 00
+11B5  5  00 00 7F 22 31
+11B6  4  8C 7F 22 31
+11B7  5  00 00 7F 22 31
+11B8  5  00 00 7F 22 31
+11BA  2  FF 5C
+11BD  5  87 1E 7F 22 31
+11C1  7  00 00 62 11 C1 00 00
+1310  2  1C 92
+1410  2  00 00
+1411  5  00 00 7F 22 12
+1412  2  00 00
+1434  1  26
+1440  2  01 89
+1441  5  00 00 7F 22 12
+1442  2  01 88
+1445  2  01 8F
+1446  2  00 16
+1447  2  00 34
+1448  2  00 11
+1450  2  00 00
+1451  2  00 00