Migrate from Claude Code to OpenCode structure

- Move legacy content to legacy/ folder (old, old2, docs, learnings, scripts)
- Create new .opencode/ structure with skills/, tools/, agents/ folders
- Update Makefile to symlink to ~/.config/opencode/ instead of ~/.claude/
- Update Makefile to manage skills, tools, and agents (remove settings.json)
- Simplify install/uninstall (no backup logic)
- Add README.md documenting the new structure
- Keep settings.json as historical reference

legacy/old2/skills/examples/simple-workflow.md

@@ -0,0 +1,71 @@
+# Example: Simple Workflow Skill
+
+A basic skill with just a SKILL.md file - no scripts or reference files needed.
+
+## Structure
+
+```
+skills/list-open-prs/
+└── SKILL.md
+```
+
+## When to Use
+
+- Skill is simple (<300 lines)
+- No error-prone bash operations
+- No need for reference documentation
+- Straightforward workflow
+
+## Example: list-open-prs
+
+```markdown
+---
+name: list-open-prs
+description: >
+  List all open pull requests for the current repository.
+  Use when user wants to see PRs or says /list-open-prs.
+model: haiku
+user-invocable: true
+---
+
+# List Open PRs
+
+@~/.claude/skills/gitea/SKILL.md
+
+Show all open pull requests in the current repository.
+
+## Process
+
+1. **Get repository info**
+   - `git remote get-url origin`
+   - Parse owner/repo from URL
+
+2. **Fetch open PRs**
+   - `tea pulls list --state open --output simple`
+
+3. **Format results** as table
+
+| PR # | Title | Author | Created |
+|------|-------|--------|---------|
+| ... | ... | ... | ... |
+
+## Guidelines
+
+- Show most recent PRs first
+- Include link to each PR
+- If no open PRs, say "No open pull requests"
+```
+
+## Why This Works
+
+- **Concise**: Entire skill fits in ~30 lines
+- **Simple commands**: Just git and tea CLI
+- **No error handling needed**: tea handles errors gracefully
+- **Structured output**: Table format is clear
+
+## What Makes It Haiku-Friendly
+
+- ✓ Simple sequential steps
+- ✓ Clear commands with no ambiguity
+- ✓ Structured output format
+- ✓ No complex decision-making