docs: ASCII typography and style normalization across all repo text

Replace every em dash with real punctuation (rewrites, not hyphen swaps)
in docs, code comments, scripts, configs, and the port records; convert
en dashes, curly quotes, ellipsis glyphs, arrows, and section signs to
ASCII; drop machine-writing tell phrases from living docs. ADR titles
now use a colon. The M2 bring-up DTS model string carried an em dash
into the patch series and its record echoes; fixed at both, and the full
series re-verified to apply cleanly onto pristine 6.18.46. One comment
in freshness.h deliberately names the em dash glyph the UI renders as
the unknown mark; that is data, kept as prose naming it.

Verified: cargo tests (sim, config-lint, rs485-bridge), shellcheck,
both driver MC/DC harnesses, patches-apply.

docs/decisions/0002-mcdc-tiering.md

@@ -1,4 +1,4 @@
-# ADR 0002 — Tiered MC/DC
+# ADR 0002: Tiered MC/DC
 
 **Status:** Accepted (2026-08-25).
 
@@ -11,23 +11,23 @@ that code would be theatre, not assurance.
 ## Decision
 A **two-tier** policy, measured against the Hardware Abstraction Seam:
 
-- **Tier 1 — our own hardware-facing code → real 100% MC/DC.** `modbus_engine.c`,
+- **Tier 1, our own hardware-facing code -> real 100% MC/DC.** `modbus_engine.c`,
   `relays.c`, `warden_rga.c` (wrapper), `hpmcu.rs`, `devmem.rs`, `freshness.c`, plus
   the two smallest near-mainline drivers where feasible. Enforced in CI
   (`gcc-14 -fcondition-coverage` + `gcov-14 --conditions`). Rust uses
-  `cargo-llvm-cov` line/region coverage for now — true `--mcdc` needs a nightly
+  `cargo-llvm-cov` line/region coverage for now; true `--mcdc` needs a nightly
   toolchain (`-Z coverage-options=condition`) and is deferred on that tooling skew;
   the C drivers carry the literal MC/DC gate.
-- **Tier 2 — ported/vendor drivers → fault-injection + branch coverage + benchmarks**
+- **Tier 2, ported/vendor drivers -> fault-injection + branch coverage + benchmarks**
   against the simulator, behind a stable seam. Explicitly NOT literal MC/DC.
 
 ## Consequences
 - Matches the user's framing: "as many drivers as possible at 100% MC/DC; for the
   rest, a very serious testing and benchmarking system."
 - The seam is the shared object: the same thing MC/DC is measured against and the
-  simulator implements — the two goals reinforce, not duplicate.
+  simulator implements; the two goals reinforce, not duplicate.
 - Every Tier-1 file gets a `drivers/<name>/test/` host harness (a `Makefile` +
-  `test_<name>.c`) that calls the one shared `drivers/enforce-mcdc.sh` — which derives
+  `test_<name>.c`) that calls the one shared `drivers/enforce-mcdc.sh`, which derives
   the driver name from the `.gcov` file, so there is a single gate to maintain, not a
   per-driver copy. The CI `mcdc` job auto-discovers any `drivers/*/test/Makefile` and
   fails below 100%.