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/tests/clock-sanity.sh

@@ -2,7 +2,7 @@
 # Clock-sanity scenario (issue #3 regression guard): boot the VM, run the
 # musl-static clockprobe in the guest, and assert the vDSO monotonic RATE
 # matches the kernel's /proc/uptime within 1%. Under QEMU -M virt this passes
-# on the current kernel (measured 0.99963) — a regression here means the
+# on the current kernel (measured 0.99963): a regression here means the
 # generic vDSO path broke. The RV1106 *board* leg of issue #3 is a separate,
 # bench-only measurement; this scenario cannot see board-specific CNTFRQ or
 # CNTVOFF misprogramming.
@@ -21,7 +21,7 @@ if [ -z "$ZIMAGE" ] || [ ! -f "$ZIMAGE" ]; then
   exit 1
 fi
 command -v qemu-system-arm >/dev/null || {
-  echo "FATAL: qemu-system-arm not on PATH — see qemu/README.md" >&2
+  echo "FATAL: qemu-system-arm not on PATH: see qemu/README.md" >&2
   exit 1
 }
 command -v arm-linux-gnueabihf-gcc >/dev/null || {
@@ -58,7 +58,7 @@ for _attempt in 1 2 3; do
   sleep 3
   kill -0 "$QEMU_PID" 2>/dev/null && break
   if grep -aq 'Could not set up host forwarding' "$WORK/console.log"; then
-    echo "== hostfwd port collision on base $PORT — retrying"
+    echo "== hostfwd port collision on base $PORT, retrying"
     QEMU_PID=""
     continue
   fi