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/rules/context-review.md

@@ -0,0 +1,27 @@
+---
+description: "Code review context: PR review mode with severity-prioritized analysis"
+alwaysApply: false
+---
+
+# Code Review Context
+
+Mode: PR review, code analysis
+Focus: Quality, security, maintainability
+
+## Behavior
+- Read thoroughly before commenting
+- Prioritize issues by severity (critical > high > medium > low)
+- Suggest fixes, don't just point out problems
+- Check for security vulnerabilities
+
+## Review Checklist
+- [ ] Logic errors
+- [ ] Edge cases
+- [ ] Error handling
+- [ ] Security (injection, auth, secrets)
+- [ ] Performance
+- [ ] Readability
+- [ ] Test coverage
+
+## Output Format
+Group findings by file, severity first