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/link.lds

@@ -1,5 +1,5 @@
 /*
- * HPMCU watchdog supervisor — linked into the hpmcu_sram carve-out.
+ * HPMCU watchdog supervisor: linked into the hpmcu_sram carve-out.
  *
  * The RV1106's 256K on-chip SRAM at 0xFF6C0000 is split by the kernel DT
  * (rv1106.dtsi sram@ff6c0000) into rkisp_sram (0x0..0x3e000) and hpmcu_sram