Revert "feat(ecc): prune plugin 43→12 items, promote 7 rules to .claude/rules/ (#245)"

This reverts commit 1bd68ff534.

.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.