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

ECC community plugin pruning: removed 530+ non-essential files
(.cursor/, .opencode/, docs/ja-JP, docs/zh-CN, docs/zh-TW,
language-specific skills/agents/rules). Retained 4 agents,
3 commands, 5 skills. Promoted 13 rule files (8 common + 5
typescript) to .claude/rules/ for CC native loading. Extracted
reusable patterns to EXTRACTED-PATTERNS.md.

.cursor/rules/golang-security.md

@@ -1,34 +0,0 @@
----
-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()
-```