feat: add Cursor IDE support with pre-translated configs

Add complete .cursor/ directory with rules, agents, skills, commands,
and MCP config adapted for Cursor's format. This makes ecc-universal
a truly cross-IDE package supporting Claude Code, Cursor, and OpenCode.

- 27 rule files with YAML frontmatter (description, globs, alwaysApply)
- 13 agent files with full model IDs and readonly flags
- 30 skill directories (identical Agent Skills standard, no translation)
- 31 command files (5 multi-* stubbed for missing codeagent-wrapper)
- MCP config with Cursor env interpolation syntax
- README.md and MIGRATION.md documentation
- install.sh --target cursor flag for project-scoped installation
- package.json updated with .cursor/ in files and cursor keywords

.cursor/commands/update-docs.md

@@ -0,0 +1,31 @@
+# Update Documentation
+
+Sync documentation from source-of-truth:
+
+1. Read package.json scripts section
+   - Generate scripts reference table
+   - Include descriptions from comments
+
+2. Read .env.example
+   - Extract all environment variables
+   - Document purpose and format
+
+3. Generate docs/CONTRIB.md with:
+   - Development workflow
+   - Available scripts
+   - Environment setup
+   - Testing procedures
+
+4. Generate docs/RUNBOOK.md with:
+   - Deployment procedures
+   - Monitoring and alerts
+   - Common issues and fixes
+   - Rollback procedures
+
+5. Identify obsolete documentation:
+   - Find docs not modified in 90+ days
+   - List for manual review
+
+6. Show diff summary
+
+Single source of truth: package.json and .env.example