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-patterns.md

@@ -1,36 +0,0 @@
----
-description: "Common design patterns: skeleton projects, repository pattern, API response format"
-alwaysApply: true
----
-
-# Common Patterns
-
-## Skeleton Projects
-
-When implementing new functionality:
-1. Search for battle-tested skeleton projects
-2. Use parallel agents to evaluate options:
-   - Security assessment
-   - Extensibility analysis
-   - Relevance scoring
-   - Implementation planning
-3. Clone best match as foundation
-4. Iterate within proven structure
-
-## Design Patterns
-
-### Repository Pattern
-
-Encapsulate data access behind a consistent interface:
-- Define standard operations: findAll, findById, create, update, delete
-- Concrete implementations handle storage details (database, API, file, etc.)
-- Business logic depends on the abstract interface, not the storage mechanism
-- Enables easy swapping of data sources and simplifies testing with mocks
-
-### API Response Format
-
-Use a consistent envelope for all API responses:
-- Include a success/status indicator
-- Include the data payload (nullable on error)
-- Include an error message field (nullable on success)
-- Include metadata for paginated responses (total, page, limit)