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-dev.md

@@ -0,0 +1,25 @@
+---
+description: "Development context: active coding mode with implementation-first priorities"
+alwaysApply: false
+---
+
+# Development Context
+
+Mode: Active development
+Focus: Implementation, coding, building features
+
+## Behavior
+- Write code first, explain after
+- Prefer working solutions over perfect solutions
+- Run tests after changes
+- Keep commits atomic
+
+## Priorities
+1. Get it working
+2. Get it right
+3. Get it clean
+
+## Tools to favor
+- Edit, Write for code changes
+- Bash for running tests/builds
+- Grep, Glob for finding code