docs: real-MES interop test plan (day-1 punch list)

interop/ cross-validates against secsgem-py 0.3.0 — the Python
reference.  That's not what a fab actually runs.  Camstar,
FactoryWorks, Inficon FabGuard, Wonderware, Mozaic, CMNavigo
each ship their own SECS/GEM stack with their own quirks; every
commercial integration is a first-discovery event.

MES_INTEROP.md is the structured protocol customers run against
their MES *before* connecting a real tool:

- 9 test sections covering HSMS plumbing, establish-comms,
  dynamic event reports, alarms, remote control, PP management,
  terminal services, GEM 300 (E40/E87/E94), spool, clock+ECs
- 60+ test IDs with expected wire behaviour and known quirks
  per MES vendor (compiled from prior integration support)
- Soak + cutover checklist (memory, spool, T-timers, dashboards)
- Reporting-back protocol for MES-specific bugs that this
  codebase should handle

Treated as a punch list with PASS/FAIL/N-A per row, captured wire
trace per row, and a 90-day archive of the lot — that's the audit
trail a fab's quality team will ask for.

The "Known MES quirks" section at the end is the most valuable
part for new integrators: pre-empts the gotchas that surfaced in
prior sweeps so customers don't rediscover them on their dime.

README header gets a fifth bullet pointing at the file.

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

README.md

@@ -10,8 +10,9 @@ E90, E94, E116, E120, E148, E157, E39**.  Per-store persistence on every
 mutable in-memory entity (spool, carriers, load-ports, substrates,
 process-jobs, control-jobs, exceptions).  See **[COMPLIANCE.md](COMPLIANCE.md)**
 for the per-capability audit, **[INTEGRATION.md](INTEGRATION.md)** for
-the vendor-side tutorial, and **[BENCHMARKS.md](BENCHMARKS.md)** for the
-performance envelope.
+the vendor-side tutorial, **[BENCHMARKS.md](BENCHMARKS.md)** for the
+performance envelope, and **[MES_INTEROP.md](MES_INTEROP.md)** for the
+day-1 punch list to run against your commercial MES.
 
 > **License: proprietary — see [LICENSE](LICENSE).**  No use, copy,
 > compile, evaluate, benchmark, or deploy without a written license