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.

contexts/dev.md

@@ -1,20 +0,0 @@
-# Development Context
-
-Mode: Active development
-Focus: Implementation, coding, building features
-
-## Behavior
-- Write code first, explain after
-- Prefer working solutions over perfect solutions
-- Run tests after changes
-- Keep commits atomic
-
-## Priorities
-1. Get it working
-2. Get it right
-3. Get it clean
-
-## Tools to favor
-- Edit, Write for code changes
-- Bash for running tests/builds
-- Grep, Glob for finding code

contexts/research.md

@@ -1,26 +0,0 @@
-# Research Context
-
-Mode: Exploration, investigation, learning
-Focus: Understanding before acting
-
-## Behavior
-- Read widely before concluding
-- Ask clarifying questions
-- Document findings as you go
-- Don't write code until understanding is clear
-
-## Research Process
-1. Understand the question
-2. Explore relevant code/docs
-3. Form hypothesis
-4. Verify with evidence
-5. Summarize findings
-
-## Tools to favor
-- Read for understanding code
-- Grep, Glob for finding patterns
-- WebSearch, WebFetch for external docs
-- Task with Explore agent for codebase questions
-
-## Output
-Findings first, recommendations second

contexts/review.md

@@ -1,22 +0,0 @@
-# Code Review Context
-
-Mode: PR review, code analysis
-Focus: Quality, security, maintainability
-
-## Behavior
-- Read thoroughly before commenting
-- Prioritize issues by severity (critical > high > medium > low)
-- Suggest fixes, don't just point out problems
-- Check for security vulnerabilities
-
-## Review Checklist
-- [ ] Logic errors
-- [ ] Edge cases
-- [ ] Error handling
-- [ ] Security (injection, auth, secrets)
-- [ ] Performance
-- [ ] Readability
-- [ ] Test coverage
-
-## Output Format
-Group findings by file, severity first