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.

.opencode/commands/learn.md

@@ -1,61 +0,0 @@
----
-description: Extract patterns and learnings from current session
-agent: build
----
-
-# Learn Command
-
-Extract patterns, learnings, and reusable insights from the current session: $ARGUMENTS
-
-## Your Task
-
-Analyze the conversation and code changes to extract:
-
-1. **Patterns discovered** - Recurring solutions or approaches
-2. **Best practices applied** - Techniques that worked well
-3. **Mistakes to avoid** - Issues encountered and solutions
-4. **Reusable snippets** - Code patterns worth saving
-
-## Output Format
-
-### Patterns Discovered
-
-**Pattern: [Name]**
-- Context: When to use this pattern
-- Implementation: How to apply it
-- Example: Code snippet
-
-### Best Practices Applied
-
-1. [Practice name]
-   - Why it works
-   - When to apply
-
-### Mistakes to Avoid
-
-1. [Mistake description]
-   - What went wrong
-   - How to prevent it
-
-### Suggested Skill Updates
-
-If patterns are significant, suggest updates to:
-- `skills/coding-standards/SKILL.md`
-- `skills/[domain]/SKILL.md`
-- `rules/[category].md`
-
-## Instinct Format (for continuous-learning-v2)
-
-```json
-{
-  "trigger": "[situation that triggers this learning]",
-  "action": "[what to do]",
-  "confidence": 0.7,
-  "source": "session-extraction",
-  "timestamp": "[ISO timestamp]"
-}
-```
-
----
-
-**TIP**: Run `/learn` periodically during long sessions to capture insights before context compaction.