docs: remove common-cache references from documentation and tooling

Remove all remaining references to common-cache from project documentation,
test workflows, and build tooling after action deletion.

Updated:
- CLAUDE.md: Remove from action catalog (28 → 27 actions)
- README.md: Regenerate catalog without common-cache
- SECURITY.md: Update caching optimization notes
- Test workflows: Remove common-cache test references
- spec_helper.sh: Remove common-cache test helpers
- generate_listing.cjs: Remove from category/language mappings
- update-validators.py: Remove custom validator entry

_tests/unit/spec_helper.sh

@@ -92,10 +92,6 @@ setup_default_inputs() {
   "go-build" | "go-lint")
     [[ "$input_name" != "go-version" ]] && export INPUT_GO_VERSION="1.21"
     ;;
-  "common-cache")
-    [[ "$input_name" != "type" ]] && export INPUT_TYPE="npm"
-    [[ "$input_name" != "paths" ]] && export INPUT_PATHS="node_modules"
-    ;;
   "common-retry")
     [[ "$input_name" != "command" ]] && export INPUT_COMMAND="echo test"
     ;;
@@ -158,10 +154,6 @@ cleanup_default_inputs() {
   "go-build" | "go-lint")
     [[ "$input_name" != "go-version" ]] && unset INPUT_GO_VERSION
     ;;
-  "common-cache")
-    [[ "$input_name" != "type" ]] && unset INPUT_TYPE
-    [[ "$input_name" != "paths" ]] && unset INPUT_PATHS
-    ;;
   "common-retry")
     [[ "$input_name" != "command" ]] && unset INPUT_COMMAND
     ;;
@@ -244,11 +236,6 @@ shellspec_mock_action_run() {
     echo "build-time=45" >>"$GITHUB_OUTPUT"
     echo "platforms=linux/amd64" >>"$GITHUB_OUTPUT"
     ;;
-  "common-cache")
-    echo "cache-hit=true" >>"$GITHUB_OUTPUT"
-    echo "cache-key=Linux-npm-abc123" >>"$GITHUB_OUTPUT"
-    echo "cache-paths=node_modules" >>"$GITHUB_OUTPUT"
-    ;;
   "common-file-check")
     echo "found=true" >>"$GITHUB_OUTPUT"
     ;;