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.

build/fetch-kernel-tarball.sh

@@ -1,7 +1,7 @@
 #!/usr/bin/env bash
 # Fetch (with retries) and sha256-verify the pristine kernel tarball into $1.
 # Single source of truth for the URL + verification used by build-kernel.sh
-# and both CI jobs (patches-apply, kernel-build) — a KVER bump edits this file
+# and both CI jobs (patches-apply, kernel-build): a KVER bump edits this file
 # and build-kernel.sh only. FAILS CLOSED: a missing pin refuses to proceed.
 #
 # Usage: fetch-kernel-tarball.sh <destination-path>
@@ -17,7 +17,7 @@ TB="${1:?usage: fetch-kernel-tarball.sh <destination-path>}"
 # Pin first: a forgotten pin on a KVER bump should refuse BEFORE burning a
 # 140MB download it will then reject anyway.
 [ -f "$SHA_FILE" ] || {
-  echo "FATAL: no pinned sha256 for linux-$KVER (expected $SHA_FILE) — refusing an unverified tarball" >&2
+  echo "FATAL: no pinned sha256 for linux-$KVER (expected $SHA_FILE): refusing an unverified tarball" >&2
   exit 1
 }
 if [ ! -f "$TB" ]; then