♻️ refactor(skills): separate thirdparty skills into thirdparty/ subdirectory

- Move all third-party skills from codex/skills/ to codex/skills/thirdparty/
- Move .sources/ to codex/skills/thirdparty/.sources/
- Delete systematic-debugging/CREATION-LOG.md (internal dev note, not skill content)
- Update sync_thirdparty_skills.sh paths and conflict detection
- Update thirdparty_skills.json source_list paths
- Update install_skills_action to collect from both own and thirdparty dirs,
  logging [thirdparty] tag for third-party installs
- Update SKILLS.md directory structure docs
- Update tests to reflect new paths

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.gitea/ci/sync_thirdparty_skills.sh

@@ -101,10 +101,8 @@ PY
 
 tracked_skill_exists() {
   local name="$1"
-  if git ls-files --error-unmatch -- "codex/skills/$name" >/dev/null 2>&1; then
-    return 0
-  fi
-  return 1
+  # conflict only if a first-party SKILL.md exists directly under codex/skills/<name>/
+  [ -f "codex/skills/$name/SKILL.md" ]
 }
 
 cd "$REPO_DIR"
@@ -123,7 +121,7 @@ trap cleanup EXIT
 
 git checkout -B "$TARGET_BRANCH" "origin/$TARGET_BRANCH"
 
-mkdir -p "codex/skills/.sources"
+mkdir -p "codex/skills/thirdparty/.sources"
 
 sources_file="$tmp_dir/sources.tsv"
 if ! emit_sources_tsv > "$sources_file"; then
@@ -165,13 +163,13 @@ while IFS=$'\x1f' read -r source_id snapshot_dir sync_mode source_list skills_su
           echo "ERROR: duplicate third-party skill name: $name" >&2
           exit 1
         fi
-        if [ -d "codex/skills/$name" ] && tracked_skill_exists "$name"; then
+        if [ -d "codex/skills/thirdparty/$name" ] && tracked_skill_exists "$name"; then
           echo "ERROR: skill name conflict with tracked skill: $name" >&2
           exit 1
         fi
 
-        rm -rf "codex/skills/$name"
-        cp -R "$dir" "codex/skills/$name"
+        rm -rf "codex/skills/thirdparty/$name"
+        cp -R "$dir" "codex/skills/thirdparty/$name"
         names+=("$name")
         owners["$name"]="$source_id"
       done
@@ -182,12 +180,12 @@ while IFS=$'\x1f' read -r source_id snapshot_dir sync_mode source_list skills_su
         echo "ERROR: duplicate third-party skill name: $name" >&2
         exit 1
       fi
-      if [ -d "codex/skills/$name" ] && tracked_skill_exists "$name"; then
+      if [ -d "codex/skills/thirdparty/$name" ] && tracked_skill_exists "$name"; then
         echo "ERROR: skill name conflict with tracked skill: $name" >&2
         exit 1
       fi
 
-      render_codex_skill "$snapshot_root" "codex/skills/$name" "$platform_config" "$template_root" "$data_dir" "$scripts_dir"
+      render_codex_skill "$snapshot_root" "codex/skills/thirdparty/$name" "$platform_config" "$template_root" "$data_dir" "$scripts_dir"
       names+=("$name")
       owners["$name"]="$source_id"
       ;;

.gitea/ci/thirdparty_skills.json

@@ -6,7 +6,7 @@
       "upstream_ref": "main",
       "snapshot_dir": "superpowers",
       "sync_mode": "copy_skill_dirs",
-      "source_list": "codex/skills/.sources/superpowers.list",
+      "source_list": "codex/skills/thirdparty/.sources/superpowers.list",
       "skills_subdir": "skills",
       "remove_paths": ["skills/ui-ux-pro-max"]
     },
@@ -16,7 +16,7 @@
       "upstream_ref": "main",
       "snapshot_dir": "ui-ux-pro-max",
       "sync_mode": "render_codex_skill",
-      "source_list": "codex/skills/.sources/ui-ux-pro-max.list",
+      "source_list": "codex/skills/thirdparty/.sources/ui-ux-pro-max.list",
       "output_name": "ui-ux-pro-max",
       "platform_config": "src/ui-ux-pro-max/templates/platforms/codex.json",
       "template_root": "src/ui-ux-pro-max/templates",
@@ -29,7 +29,7 @@
       "upstream_ref": "main",
       "snapshot_dir": "andrej-karpathy-skills",
       "sync_mode": "copy_skill_dirs",
-      "source_list": "codex/skills/.sources/andrej-karpathy-skills.list",
+      "source_list": "codex/skills/thirdparty/.sources/andrej-karpathy-skills.list",
       "skills_subdir": "skills"
     }
   ]