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/mbox-roundtrip.sh

@@ -1,6 +1,6 @@
 #!/bin/sh
 # Prove the A7<->HPMCU mailbox round-trip on channel 0. Write A2B_CMD first, then
-# A2B_DAT — the A2B_DAT write is the doorbell (raises A2B_STATUS on the MCU side,
+# A2B_DAT: the A2B_DAT write is the doorbell (raises A2B_STATUS on the MCU side,
 # whose echo firmware has enabled A2B_INTEN), so both CMD and DAT are current when
 # the SCR1 reads them. The SCR1 echoes {cmd,dat} verbatim into B2A_CMD/B2A_DAT.
 CMD=${1:-0x00001234}