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/builtin/claude/src/claude_status.dart

@@ -53,8 +53,8 @@ String nextSafePermissionMode(String current) {
 }
 
 /// Status-line segments split around the permission-mode badge so the UI can
-/// render the mode as an interactive control between them (T-226). [leading]
-/// is the model; [trailing] joins context / cost / rate-limit. Either may be
+/// render the mode as an interactive control between them (T-226). `leading`
+/// is the model; `trailing` joins context / cost / rate-limit. Either may be
 /// null when there's nothing to show.
 ({String? leading, String? trailing}) statusSegmentsAroundMode(SessionStatus s) {
   final trailing = [