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.

qemu/rs485-bridge/benches/bridge_bench.rs

@@ -1,4 +1,4 @@
-//! Micro-benchmarks for the RS-485 bridge dispatch path — same dependency-free
+//! Micro-benchmarks for the RS-485 bridge dispatch path: same dependency-free
 //! fixed-iteration pattern as sim/benches/sim_bench.rs: human timings to
 //! stdout, one JSON line per benchmark to stderr for CI trend capture.
 //!