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/learn.md

@@ -0,0 +1,61 @@
+---
+description: Extract patterns and learnings from current session
+agent: build
+---
+
+# Learn Command
+
+Extract patterns, learnings, and reusable insights from the current session: $ARGUMENTS
+
+## Your Task
+
+Analyze the conversation and code changes to extract:
+
+1. **Patterns discovered** - Recurring solutions or approaches
+2. **Best practices applied** - Techniques that worked well
+3. **Mistakes to avoid** - Issues encountered and solutions
+4. **Reusable snippets** - Code patterns worth saving
+
+## Output Format
+
+### Patterns Discovered
+
+**Pattern: [Name]**
+- Context: When to use this pattern
+- Implementation: How to apply it
+- Example: Code snippet
+
+### Best Practices Applied
+
+1. [Practice name]
+   - Why it works
+   - When to apply
+
+### Mistakes to Avoid
+
+1. [Mistake description]
+   - What went wrong
+   - How to prevent it
+
+### Suggested Skill Updates
+
+If patterns are significant, suggest updates to:
+- `skills/coding-standards/SKILL.md`
+- `skills/[domain]/SKILL.md`
+- `rules/[category].md`
+
+## Instinct Format (for continuous-learning-v2)
+
+```json
+{
+  "trigger": "[situation that triggers this learning]",
+  "action": "[what to do]",
+  "confidence": 0.7,
+  "source": "session-extraction",
+  "timestamp": "[ISO timestamp]"
+}
+```
+
+---
+
+**TIP**: Run `/learn` periodically during long sessions to capture insights before context compaction.