docs: customer-ready sweep + README restructure + tshark CI fix

Audit pass over the public-facing surface so a customer can read it
end-to-end without tripping on stale numbers or self-contradictions.

README + docs accuracy:
- Test counts 426 → 445, assertions 2 557 → 2 753 (verified via
  doctest run); E5 row was missing test_e5_kat (19 cases)
- Interop checks 24 → 31, COMPLIANCE.md message count 149 → 164,
  COMPLIANCE.md "291 cases / 1515 assertions" → 445 / 2 753
- README "60+ test IDs" for MES_INTEROP → actual 59
- PVD example counts: 32 SVIDs/17 CEIDs → 29/21, "~40 handlers
  in ~200 lines" → 51 in ~460, "~700 lines" → ~1,100; main.cpp
  header table-of-contents resynced with the actual 7 sections

Out-of-scope honesty (COMPLIANCE.md §8 + FAQ.md):
- Removed HSMS-GS (was both ✅ implemented in §1 and "out of scope"
  in §8; INTEGRATION.md §7 documents using it)
- Removed multi-block SECS-I (split_message/assemble_message exist
  with 4 dedicated tests)
- Added serial-port wiring as the genuine open ⬜ item — FSM is
  tested end-to-end over TCP; only the asio serial_port glue is
  deferred
- COMPLIANCE.md intro now lists E42 and notes "E37 (SS + GS)"

README restructure:
- Moved the 8-command proof table and per-standard test-coverage
  table to a new PROOFS.md (72 lines)
- README now leads with what / Quick start / Documentation map,
  then a one-paragraph "How it's proved" linking to PROOFS.md
- Updated cross-refs in FAQ.md, GLOSSARY.md, VERIFICATION.md, and
  interop/README.md to point at PROOFS.md

CI fix — tshark-dissector job:
- interop/tshark_validate.sh hardcoded /app/build/secs_server etc.
  which only works inside the docker image.  Now derives ROOT from
  the script's own location and accepts BUILD/SERVER/CLIENT/DATA
  env overrides, so CI can run it from the workspace dir
- Verified still passes in docker (69 frames, 0 malformed)

.gitignore:
- Added build-fuzz/ and build-tsan/ (were showing as untracked)

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

GLOSSARY.md

@@ -149,7 +149,7 @@ TA3 (BUSY duration) live alongside the signals — see
 | **The router**  | `gem::Router` — `(stream, function) → handler` dispatch table.         |
 | **The codec**   | `secs2::encode` / `secs2::decode` for the wire bytes.                  |
 | **The catalog** | `data/messages.yaml` — every SECS-II message we ship, codegen'd to `messages.hpp`. |
-| **The proof**   | The 8 commands in [README.md](README.md#proof-of-feature-completeness). |
+| **The proof**   | The 8 commands in [PROOFS.md](PROOFS.md). |
 | **The bench**   | `apps/secs_bench.cpp` — single-threaded throughput / latency / memory harness. |
 | **The fuzz**    | `tests/test_robustness_fuzz.cpp` — randomized property test of the model. |