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- Keep settings.json as historical reference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/old/skills/arch-review-repo/SKILL.md

@@ -0,0 +1,79 @@
+---
+name: arch-review-repo
+description: >
+  Perform a full architecture review of the current repository. Analyzes structure,
+  patterns, dependencies, and generates prioritized recommendations. Use when reviewing
+  architecture, auditing codebase, or when user says /arch-review-repo.
+model: opus
+argument-hint:
+context: fork
+user-invocable: true
+---
+
+# Architecture Review
+
+@~/.claude/skills/software-architecture/SKILL.md
+
+## Process
+
+1. **Identify the repository**: Use the current working directory as the repository path.
+
+2. **Spawn the software-architect agent** for deep analysis:
+
+   ```
+   ANALYSIS_TYPE: repo-audit
+   TARGET: <repository-path>
+   CONTEXT: Full repository architecture review
+   ```
+
+   The agent will:
+   - Analyze directory structure and package organization
+   - Identify patterns and anti-patterns in the codebase
+   - Assess dependency graph and module boundaries
+   - Review test coverage approach
+   - Generate structured findings with prioritized recommendations
+
+3. **Present the results** to the user in this format:
+
+   ```markdown
+   ## Repository Architecture Review: <repo-name>
+
+   ### Structure: <Good|Needs Work>
+   - [Key observations about package organization]
+   - [Directory structure assessment]
+   - [Naming conventions evaluation]
+
+   ### Patterns Identified
+   - [Positive patterns found in the codebase]
+   - [Architectural styles detected (layered, hexagonal, etc.)]
+
+   ### Anti-Patterns Detected
+   - [Anti-pattern name]: [Location and description]
+   - [Anti-pattern name]: [Location and description]
+
+   ### Concerns
+   - [Specific issues that need attention]
+   - [Technical debt areas]
+
+   ### Recommendations (prioritized)
+   1. **P0 - Critical**: [Most urgent recommendation]
+   2. **P1 - High**: [Important improvement]
+   3. **P2 - Medium**: [Nice-to-have improvement]
+   4. **P3 - Low**: [Minor optimization]
+
+   ### Health Score: <A|B|C|D|F>
+   [Brief justification for the grade]
+   ```
+
+4. **Offer follow-up actions**:
+   - Create issues for critical findings
+   - Generate a detailed report
+   - Review specific components in more depth
+
+## Guidelines
+
+- Be specific: Reference exact files, packages, and locations
+- Be actionable: Every finding should have a clear path to resolution
+- Be balanced: Acknowledge what the codebase does well
+- Be proportionate: Focus on high-impact issues first
+- Stay objective: Focus on patterns and principles, not style preferences