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-security.md

@@ -0,0 +1,34 @@
+---
+description: "Go security: environment variable secrets, gosec static analysis, context timeouts"
+globs: ["**/*.go"]
+alwaysApply: false
+---
+
+# Go Security
+
+> This file extends [common/security.md](../common/security.md) with Go specific content.
+
+## Secret Management
+
+```go
+apiKey := os.Getenv("OPENAI_API_KEY")
+if apiKey == "" {
+    log.Fatal("OPENAI_API_KEY not configured")
+}
+```
+
+## Security Scanning
+
+- Use **gosec** for static security analysis:
+  ```bash
+  gosec ./...
+  ```
+
+## Context & Timeouts
+
+Always use `context.Context` for timeout control:
+
+```go
+ctx, cancel := context.WithTimeout(ctx, 5*time.Second)
+defer cancel()
+```