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/common-git-workflow.md

@@ -1,50 +0,0 @@
----
-description: "Git commit message format, PR workflow, and feature implementation workflow"
-alwaysApply: true
----
-
-# Git Workflow
-
-## Commit Message Format
-
-```
-<type>: <description>
-
-<optional body>
-```
-
-Types: feat, fix, refactor, docs, test, chore, perf, ci
-
-Note: Attribution disabled globally via ~/.claude/settings.json.
-
-## Pull Request Workflow
-
-When creating PRs:
-1. Analyze full commit history (not just latest commit)
-2. Use `git diff [base-branch]...HEAD` to see all changes
-3. Draft comprehensive PR summary
-4. Include test plan with TODOs
-5. Push with `-u` flag if new branch
-
-## Feature Implementation Workflow
-
-1. **Plan First**
-   - Use **planner** agent to create implementation plan
-   - Identify dependencies and risks
-   - Break down into phases
-
-2. **TDD Approach**
-   - Use **tdd-guide** agent
-   - Write tests first (RED)
-   - Implement to pass tests (GREEN)
-   - Refactor (IMPROVE)
-   - Verify 80%+ coverage
-
-3. **Code Review**
-   - Use **code-reviewer** agent immediately after writing code
-   - Address CRITICAL and HIGH issues
-   - Fix MEDIUM issues when possible
-
-4. **Commit & Push**
-   - Detailed commit messages
-   - Follow conventional commits format