feat: add golang-cli-app skill with code examples and install scripts

Add a comprehensive skill for Go CLI app development with:
- SKILL.md with Cobra/Viper/PTerm/Bubble Tea code examples
- TUI patterns reference for easy TUI adoption
- Subcommand design rules and naming conventions
- Install scripts for macOS/Linux and Windows

Refs: #15

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: qdriven

README.md

@@ -159,6 +159,27 @@ github_owner: your-username
 work_dir: ./workspace
 ```
 
+## Skills
+
+Spark provides AI agent skills for Go CLI app development:
+
+### golang-cli-app Skill
+
+Code templates and best practices for building Go CLI apps with Cobra/Viper/PTerm/Bubble Tea.
+
+```bash
+# Install the skill
+./skills/golang-cli-app/scripts/install.sh --system          # All agents
+./skills/golang-cli-app/scripts/install.sh --project         # Current project only
+./skills/golang-cli-app/scripts/install.sh --system --agent claude-code  # Specific agent
+```
+
+Includes:
+- SKILL.md with complete code examples (Cobra commands, Viper config, PTerm/Bubble Tea TUI)
+- TUI patterns reference (`references/tui-patterns.md`)
+- Subcommand design rules (`references/subcommand-rules.md`)
+- Install scripts for macOS/Linux and Windows
+
 ## Documentation
 
 Online docs: https://variableway.github.io/spark-cli/