docs: fix 41 unresolved dartdoc references

Convert non-resolving [refs] in doc comments to backtick code-spans across 24
lib/ files (param/field names out of doc scope, method refs on other classes,
non-API strings like regex char-classes and command ids). Verified 0
"unresolved doc reference" warnings via `dart doc --validate-links`. The
dart-doc CI gate (test.yml) never ran before — Gitea Actions was inactive — so
this debt had accumulated unchecked.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/kernel/src/keymap/modifier_tap.dart

@@ -9,8 +9,8 @@
 ///
 /// Headless and clock-injected: the caller (the root shell's raw-keyboard
 /// handler) passes the event time so it neither reads a clock nor consumes
-/// events. Feed every [KeyDownEvent] to [down] and every [KeyUpEvent] to
-/// [up], passing the event's [KeyModifier] (null for non-modifier keys).
+/// events. Feed every [KeyDownEvent] to `down` and every [KeyUpEvent] to
+/// `up`, passing the event's [KeyModifier] (null for non-modifier keys).
 library;
 
 import 'key_chord.dart';