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/rootfs/etc/rc

@@ -1,13 +1,13 @@
 #!/bin/busybox sh
 # shellcheck shell=dash
 # Stage-1 rc: sourced by /init (still PID 1, initramfs root) when a virtio
-# disk is present. Emulates U-Boot's slot choice — mount the validated slot's
+# disk is present. Emulates U-Boot's slot choice: mount the validated slot's
 # rootfs and switch_root into it. This is an EMULATION of the A/B selection
 # outcome, not the BCB/bootcount mechanism itself.
 #
 # Every guarded failure path `return`s to /init (valid in a sourced script;
 # /init then falls through to shell/poweroff). The final exec is the one
-# unguardable step: if switch_root itself fails to launch, the shell — PID 1 —
+# unguardable step: if switch_root itself fails to launch, the shell (PID 1)
 # exits and the kernel panics; the applet-existence check below catches the
 # only preventable variant of that.
 
@@ -19,22 +19,22 @@ slot="$(warden_slot)"
 
 root="/dev/block/by-name/rootfs${slot}"
 if [ ! -e "$root" ]; then
-    echo "rc: $root missing — staying in initramfs"
+    echo "rc: $root missing: staying in initramfs"
     return 0
 fi
 
 mkdir -p /mnt
 if ! mount -t ext4 "$root" /mnt; then
-    echo "rc: mount of $root failed — staying in initramfs"
+    echo "rc: mount of $root failed: staying in initramfs"
     return 0
 fi
 if [ ! -x /mnt/sbin/init ]; then
-    echo "rc: $root has no /sbin/init — staying in initramfs"
+    echo "rc: $root has no /sbin/init: staying in initramfs"
     umount /mnt
     return 0
 fi
 if ! command -v switch_root >/dev/null; then
-    echo "rc: busybox lacks switch_root — staying in initramfs"
+    echo "rc: busybox lacks switch_root: staying in initramfs"
     umount /mnt
     return 0
 fi