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.

commands/learn.md

@@ -1,70 +0,0 @@
-# /learn - Extract Reusable Patterns
-
-Analyze the current session and extract any patterns worth saving as skills.
-
-## Trigger
-
-Run `/learn` at any point during a session when you've solved a non-trivial problem.
-
-## What to Extract
-
-Look for:
-
-1. **Error Resolution Patterns**
-   - What error occurred?
-   - What was the root cause?
-   - What fixed it?
-   - Is this reusable for similar errors?
-
-2. **Debugging Techniques**
-   - Non-obvious debugging steps
-   - Tool combinations that worked
-   - Diagnostic patterns
-
-3. **Workarounds**
-   - Library quirks
-   - API limitations
-   - Version-specific fixes
-
-4. **Project-Specific Patterns**
-   - Codebase conventions discovered
-   - Architecture decisions made
-   - Integration patterns
-
-## Output Format
-
-Create a skill file at `~/.claude/skills/learned/[pattern-name].md`:
-
-```markdown
-# [Descriptive Pattern Name]
-
-**Extracted:** [Date]
-**Context:** [Brief description of when this applies]
-
-## Problem
-[What problem this solves - be specific]
-
-## Solution
-[The pattern/technique/workaround]
-
-## Example
-[Code example if applicable]
-
-## When to Use
-[Trigger conditions - what should activate this skill]
-```
-
-## Process
-
-1. Review the session for extractable patterns
-2. Identify the most valuable/reusable insight
-3. Draft the skill file
-4. Ask user to confirm before saving
-5. Save to `~/.claude/skills/learned/`
-
-## Notes
-
-- Don't extract trivial fixes (typos, simple syntax errors)
-- Don't extract one-time issues (specific API outages, etc.)
-- Focus on patterns that will save time in future sessions
-- Keep skills focused - one pattern per skill