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/golang-coding-style.md

@@ -0,0 +1,32 @@
+---
+description: "Go coding style: gofmt mandatory, small interfaces, error wrapping with context"
+globs: ["**/*.go"]
+alwaysApply: false
+---
+
+# Go Coding Style
+
+> This file extends [common/coding-style.md](../common/coding-style.md) with Go specific content.
+
+## Formatting
+
+- **gofmt** and **goimports** are mandatory — no style debates
+
+## Design Principles
+
+- Accept interfaces, return structs
+- Keep interfaces small (1-3 methods)
+
+## Error Handling
+
+Always wrap errors with context:
+
+```go
+if err != nil {
+    return fmt.Errorf("failed to create user: %w", err)
+}
+```
+
+## Reference
+
+See skill: `golang-patterns` for comprehensive Go idioms and patterns.