docs: streamline tone across reference docs

Tone pass across the non-tutorial markdown — README, PROOFS,
ARCHITECTURE, BENCHMARKS, COMPLIANCE, FAQ, MES_INTEROP, SECURITY,
and interop/README.  Three patterns came out:

- Bug-history war stories ("Past interop sweeps surfaced…",
  "What these harnesses caught: 1. Strict U-width parsing…").
- Chat-with-reader framing ("Don't skip TLS unless…", "Treat as a
  punch list", "If you're running in a pod…", "Misconfiguration
  incidents drop dramatically").
- Self-referential narration ("we ship", "our codec", "the
  codebase's most-tested layer", "three orders of magnitude above
  fab load", "the gift that keeps giving").

README also drops the standalone ThreadSanitizer subsection under
Build details (now a single line under the new Testing section).

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

docs/PROOFS.md

@@ -1,9 +1,7 @@
-# Proof of feature-completeness
+# Proofs
 
-"Feature-complete" is a claim that the code must prove, not the
-README.  These eight commands are the proof.  If they all exit zero
-on a fresh clone, the codebase implements what
-[COMPLIANCE.md](COMPLIANCE.md) claims.
+Eight commands.  If they all exit zero on a fresh clone, the codebase
+implements what [COMPLIANCE.md](COMPLIANCE.md) claims.
 
 | # | Command                                                                                          | What it proves                                                                              |
 |---|--------------------------------------------------------------------------------------------------|---------------------------------------------------------------------------------------------|
@@ -16,11 +14,9 @@ on a fresh clone, the codebase implements what
 | 7 | `bash interop/secs4j_validate.sh`                                                                | **55 cross-validation checks** PASS against [secs4java8](https://github.com/kenta-shimizu/secs4java8) (independent Java implementation), covering S1/S2/S3/S5/S6/S7/S10/S14/S16, the full E40 PJ body, dynamic event reports + unsolicited S6F11 / S5F1 observation, alarm management, spool, PP management, terminal services, limits, trace, E39, and the GEM 300 streams secsgem-py couldn't easily drive |
 | 8 | `cmake -B build-fuzz -DSECSGEM_FUZZ=ON && build-fuzz/fuzz_secs2_decode -max_total_time=60`        | **200 000+ random inputs** through `secs2::decode`, **1.4 M+** through `try_parse_sml` per 60 s lane, ASan + UBSan + libFuzzer coverage, **0 crashes** |
 
-Plus, on every push to `main`, [Gitea Actions](.gitea/workflows/ci.yml)
-runs both a **Release build + full test suite** and a separate
-**ThreadSanitizer lane** that builds with `-fsanitize=thread` and
-fails on any race.  All 445 cases / 2 753 assertions pass under TSan
-clean.
+CI ([Gitea Actions](.gitea/workflows/ci.yml)) runs a Release build +
+full suite and a separate `-fsanitize=thread` lane on every push to
+`main`.  All 445 cases / 2 753 assertions pass under TSan clean.
 
 ## Per-standard test coverage
 
@@ -47,26 +43,24 @@ Every claimed standard has dedicated tests.  Counts are
 | Persistence + cross-cutting       | `test_job_persistence`, `test_persistence_upgrade`, `test_wire_ceid_emission`, `test_gem300_scenario`, `test_live_gem300`, `test_thread_safety`, `test_metrics_prometheus`, `test_robustness_fuzz` |  32 |
 | **Total**                          |                                                                                            | **445** |
 
-A single command to see this live: `docker compose run --rm builder
-/app/build/secsgem_tests --list-test-cases | wc -l` (currently 445).
+`docker compose run --rm builder /app/build/secsgem_tests --list-test-cases | wc -l`
+currently reports 445.
 
-## What each proof actually demonstrates
+## Categories of evidence
 
-The eight commands above split into four kinds of evidence:
+The eight commands split into four kinds:
 
-- **Internal** (#1, #2, #4, #5) — our code testing our code: unit
-  suite, conformance harness, soak property test, config validator.
-  Necessary but not independent.
-- **External, second implementation** (#3, #7) — round-trip against
-  secsgem-py 0.3.0 (Python) and secs4java8 (Java).  Two independent
-  SECS implementations must agree with us on every frame.
+- **Internal** (#1, #2, #4, #5) — unit suite, conformance harness,
+  soak property test, config validator.  Necessary but not
+  independent.
+- **External, second implementation** (#3, #7) — secsgem-py (Python)
+  and secs4java8 (Java).  Two independent SECS implementations agree
+  on every frame.
 - **External, third codec** (#6) — Wireshark's HSMS dissector,
-  written by network-protocol authors who don't share code with
-  either of us.  Catches framing bugs the implementations might both
-  share.
+  written by network-protocol authors with no shared code.  Catches
+  framing bugs the implementations might share.
 - **External, structural search** (#8) — libFuzzer + ASan + UBSan
-  exploring the decoder and SML parser surface for crashes, memory
-  errors, and UB.
+  over the decoder and SML parser surface.
 
-See [VERIFICATION.md](VERIFICATION.md) for the full test plan and
-the rationale for each external validator.
+[VERIFICATION.md](VERIFICATION.md) covers each external validator in
+detail.