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/lib.sh

@@ -9,7 +9,7 @@ qemu_log() { printf '\033[36m== %s\033[0m\n' "$*"; }
 
 # Fetch (or accept via $BUSYBOX) the pinned static armv7 busybox and verify it
 # against qemu/busybox.sha256. FAILS CLOSED: a missing pin refuses to build,
-# never silently skips verification — mirroring build/build-kernel.sh's
+# never silently skips verification, mirroring build/build-kernel.sh's
 # tarball handling. Sets $BB to the verified binary's path.
 qemu_get_busybox() {
   local sha_file="$QEMU_DIR/busybox.sha256"
@@ -19,7 +19,7 @@ qemu_get_busybox() {
   # Pin first: a missing pin refuses BEFORE downloading, same ordering as
   # build/fetch-kernel-tarball.sh.
   [ -f "$sha_file" ] || {
-    echo "FATAL: no pinned sha256 for busybox (expected $sha_file) — refusing to build from an unverified binary" >&2
+    echo "FATAL: no pinned sha256 for busybox (expected $sha_file): refusing to build from an unverified binary" >&2
     exit 1
   }
   if [ ! -f "$BB" ]; then