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.

kernel/rv1106-enablement/mailbox/scr1-echo/load-echo-fw.sh

@@ -14,7 +14,7 @@
 FW=${1:-/userdata/echo-fw-words.txt}
 
 # GRF uncached peripheral window (covers CRU + this SRAM + the mailbox
-# 0xff5c0000) — WITHOUT this the MCU's peripheral/SRAM accesses are cached and
+# 0xff5c0000): WITHOUT this the MCU's peripheral/SRAM accesses are cached and
 # invisible to Linux. hpmcu.rs: GRF_BASE 0xff040000 +0x24/+0x28 = 0xff000/0xffc00.
 devmem 0xff040024 32 0xff000
 devmem 0xff040028 32 0xffc00