docs: drop COMPLIANCE §8 "out of scope" and broaden §7 to all 4 validators

§8 was carrying two items that neither read as "deliberately out of
scope" nor matched the framing of the section:

- Equipment Processing States — E30 §6.3 explicitly leaves concrete
  states tool-defined.  The framework ships the ControlTransitionTable
  engine and YAML loader; vendors supply IDLE/SETUP/READY/EXECUTING.
  That's a design choice, not a gap.  §3 line 94 already documents
  it.
- Serial-port wiring for SECS-I — the FSM is implemented and tested
  end-to-end over TCP; only the asio serial_port adapter is missing.
  That's deferred, not out of scope.  §1a line 64 already lists it
  with status ⬜.

So §8 is dropped, §9 renumbers to §8, and the deferred follow-up
gets its own short section in the README so customers know it's
tracked without sounding defensive.

§7 used to be titled "Interoperability with secsgem-py 0.3.0" and
mentioned only that one external implementation.  We now have four
external validators (secsgem-py + secs4java8 + tshark dissector +
libFuzzer), so the section is renamed "Interoperability with
external implementations" and broadened to cover all of them with
their actual check counts.  Stale "24 named checks" updated to the
current 31; "three consecutive clean runs" line dropped as
audit-language no longer earning its keep now that it's a CI step.

FAQ's "What's not implemented?" answer rewritten to point at the
README "Deferred follow-ups" section and COMPLIANCE §8 (new
numbering), with a brief note explaining that Equipment Processing
States are spec-by-design tool-defined.

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

README.md

@@ -191,6 +191,23 @@ tool.
 
 ---
 
+## Deferred follow-ups
+
+Non-shipped pieces that aren't behavioural gaps in the spec coverage
+— each one is a small, well-defined extension on top of the existing
+runtime.  Listed here so reviewers don't go looking for them in
+[COMPLIANCE.md](COMPLIANCE.md) and find an "out of scope" entry that
+sounds defensive.
+
+- **asio `serial_port` adapter for SECS-I.**  The SECS-I FSM
+  (`secsi::Protocol`) is implemented and tested end-to-end over the
+  asio TCP transport (`secsi::TcpTransport`).  The serial driver —
+  a `serial_port` mirror of `TcpTransport`, a few hundred lines —
+  hasn't been written.  Most modern GEM equipment runs HSMS, so this
+  has been deprioritised; mirror `TcpTransport` to add it.
+
+---
+
 ## Build details
 
 The toolchain image (`Dockerfile`) is Ubuntu 24.04 with `g++-13`,