docs(shared): add the missing language-switcher row to the CIBG gap register (RB-32)

The register at libs/shared/docs/cibg-gaps.mdx had 8 rows for 9
CIBG-GAP EXTENSION markers in code. language-switcher carries a
well-formed marker with no matching row, exactly as ADR-C-008 and
adr-c-007.md's handoff note flag. Add the row from the component's
own marker comment.

Also add a small guard to check-tokens.sh (folded into check:tokens,
as ADR-C-008 suggests as an optional step): it diffs the marker set
in code against the register's rows and fails CI on drift. Verified
working with a scratch marker file before removing it.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

scripts/check-tokens.sh

@@ -18,3 +18,17 @@ if [ -n "$hits" ]; then
   exit 1
 fi
 echo 'OK: no hardcoded colours in components'
+
+# ADR-C-008 guard: every `// CIBG-GAP EXTENSION:` marker (ADR-0003 §Consequences)
+# must have a row in the register, so the table cannot drift from the code
+# again without CI catching it.
+gap_register='libs/shared/docs/cibg-gaps.mdx'
+markers=$(grep -rl 'CIBG-GAP EXTENSION' apps libs --include='*.component.ts' | xargs -n1 dirname | xargs -n1 basename | sort -u)
+rows=$(grep -oP '^\| `\K[^`]+' "$gap_register" | sort -u)
+missing=$(comm -23 <(echo "$markers") <(echo "$rows"))
+if [ -n "$missing" ]; then
+  echo "$missing"
+  echo "FAIL: CIBG-GAP EXTENSION marker(s) with no row in $gap_register"
+  exit 1
+fi
+echo 'OK: every CIBG-GAP EXTENSION marker has a cibg-gaps.mdx row'