feat: Enhance Marketplace and Skill Management UI with improved error handling and user feedback

- Updated MarketplaceDrawer to include security notes and manual installation hints.
- Refactored SkillDetailDrawer to display default icons for skills.
- Simplified SkillListItem to use default icons for better readability.
- Integrated gateway status checks and warnings in SkillsPage for improved user awareness.
- Enhanced error handling for skill installation and fetching, providing clearer feedback to users.
- Added new translations for error messages and gateway warnings to improve localization support.

build/preinstalled-skills/self-improving-agent/scripts/activator.sh

@@ -0,0 +1,20 @@
+#!/bin/bash
+# Self-Improvement Activator Hook
+# Triggers on UserPromptSubmit to remind Claude about learning capture
+# Keep output minimal (~50-100 tokens) to minimize overhead
+
+set -e
+
+# Output reminder as system context
+cat << 'EOF'
+<self-improvement-reminder>
+After completing this task, evaluate if extractable knowledge emerged:
+- Non-obvious solution discovered through investigation?
+- Workaround for unexpected behavior?
+- Project-specific pattern learned?
+- Error required debugging to resolve?
+
+If yes: Log to .learnings/ using the self-improvement skill format.
+If high-value (recurring, broadly applicable): Consider skill extraction.
+</self-improvement-reminder>
+EOF