feat: add Skill Hub feature for managing community skills

- Implemented Skill Hub page with tabs for remote, local, and installed skills.
- Added localization support for Chinese in skill-hub.json.
- Created API routes for fetching remote skills, listing local skills, and managing installed skills.
- Developed functionality for installing and uninstalling skills from both remote and local sources.
- Introduced caching mechanism for remote skills and handling updates for installed skills.

ccw/frontend/src/locales/en/skill-hub.json

@@ -0,0 +1,42 @@
+{
+  "skillHub.title": "Skill Hub",
+  "skillHub.description": "Discover and install shared skills from the community",
+  "skillHub.source.remote": "Remote",
+  "skillHub.source.local": "Local",
+  "skillHub.status.installed": "Installed",
+  "skillHub.status.updateAvailable": "Update Available",
+  "skillHub.tabs.remote": "Remote",
+  "skillHub.tabs.local": "Local",
+  "skillHub.tabs.installed": "Installed",
+  "skillHub.stats.remote": "Remote Skills",
+  "skillHub.stats.remoteDesc": "Available from community",
+  "skillHub.stats.local": "Local Skills",
+  "skillHub.stats.localDesc": "Shared locally",
+  "skillHub.stats.installed": "Installed",
+  "skillHub.stats.installedDesc": "Skills in use",
+  "skillHub.stats.updates": "Updates",
+  "skillHub.stats.updatesDesc": "New versions available",
+  "skillHub.search.placeholder": "Search skills...",
+  "skillHub.filter.allCategories": "All Categories",
+  "skillHub.actions.refresh": "Refresh",
+  "skillHub.actions.install": "Install",
+  "skillHub.actions.installing": "Installing...",
+  "skillHub.actions.update": "Update",
+  "skillHub.actions.uninstall": "Uninstall",
+  "skillHub.actions.viewDetails": "View Details",
+  "skillHub.card.tags": "Tags",
+  "skillHub.card.updated": "Updated: {date}",
+  "skillHub.install.success": "Skill '{name}' installed successfully",
+  "skillHub.install.error": "Failed to install skill: {error}",
+  "skillHub.uninstall.success": "Skill '{name}' uninstalled",
+  "skillHub.uninstall.error": "Failed to uninstall skill: {error}",
+  "skillHub.refresh.success": "Skill list refreshed",
+  "skillHub.details.comingSoon": "Details view coming soon",
+  "skillHub.error.loadFailed": "Failed to load skills. Check network connection.",
+  "skillHub.empty.remote.title": "No Remote Skills",
+  "skillHub.empty.remote.description": "Remote skill repository is empty or unreachable.",
+  "skillHub.empty.local.title": "No Local Skills",
+  "skillHub.empty.local.description": "Add skills to ~/.ccw/skill-hub/local/ to share them.",
+  "skillHub.empty.installed.title": "No Installed Skills",
+  "skillHub.empty.installed.description": "Install skills from Remote or Local tabs to use them."
+}