feat: complete OpenCode plugin support with hooks, tools, and commands

Major OpenCode integration overhaul:

- llms.txt: Comprehensive OpenCode documentation for LLMs (642 lines)
- .opencode/plugins/ecc-hooks.ts: All Claude Code hooks translated to OpenCode's plugin system
- .opencode/tools/*.ts: 3 custom tools (run-tests, check-coverage, security-audit)
- .opencode/commands/*.md: All 24 commands in OpenCode format
- .opencode/package.json: npm package structure for opencode-ecc
- .opencode/index.ts: Main plugin entry point

- Delete incorrect LIMITATIONS.md (hooks ARE supported via plugins)
- Rewrite MIGRATION.md with correct hook event mapping
- Update README.md OpenCode section to show full feature parity

OpenCode has 20+ events vs Claude Code's 3 phases:
- PreToolUse → tool.execute.before
- PostToolUse → tool.execute.after
- Stop → session.idle
- SessionStart → session.created
- SessionEnd → session.deleted
- Plus: file.edited, file.watcher.updated, permission.asked, todo.updated

- 12 agents: Full parity
- 24 commands: Full parity (+1 from original 23)
- 16 skills: Full parity
- Hooks: OpenCode has MORE (20+ events vs 3 phases)
- Custom Tools: 3 native OpenCode tools

The OpenCode configuration can now be:
1. Used directly: cd everything-claude-code && opencode
2. Installed via npm: npm install opencode-ecc

.opencode/commands/update-docs.md

@@ -0,0 +1,67 @@
+---
+description: Update documentation for recent changes
+agent: doc-updater
+subtask: true
+---
+
+# Update Docs Command
+
+Update documentation to reflect recent changes: $ARGUMENTS
+
+## Your Task
+
+1. **Identify changed code** - `git diff --name-only`
+2. **Find related docs** - README, API docs, guides
+3. **Update documentation** - Keep in sync with code
+4. **Verify accuracy** - Docs match implementation
+
+## Documentation Types
+
+### README.md
+- Installation instructions
+- Quick start guide
+- Feature overview
+- Configuration options
+
+### API Documentation
+- Endpoint descriptions
+- Request/response formats
+- Authentication details
+- Error codes
+
+### Code Comments
+- JSDoc for public APIs
+- Complex logic explanations
+- TODO/FIXME cleanup
+
+### Guides
+- How-to tutorials
+- Architecture decisions (ADRs)
+- Troubleshooting guides
+
+## Update Checklist
+
+- [ ] README reflects current features
+- [ ] API docs match endpoints
+- [ ] JSDoc updated for changed functions
+- [ ] Examples are working
+- [ ] Links are valid
+- [ ] Version numbers updated
+
+## Documentation Quality
+
+### Good Documentation
+- Accurate and up-to-date
+- Clear and concise
+- Has working examples
+- Covers edge cases
+
+### Avoid
+- Outdated information
+- Missing parameters
+- Broken examples
+- Ambiguous language
+
+---
+
+**IMPORTANT**: Documentation should be updated alongside code changes, not as an afterthought.