feat: add self-improving-agent plugin — auto-memory curation for Claude Code (#260)

New plugin: engineering-team/self-improving-agent/
- 5 skills: /si:review, /si:promote, /si:extract, /si:status, /si:remember
- 2 agents: memory-analyst, skill-extractor
- 1 hook: PostToolUse error capture (zero overhead on success)
- 3 reference docs: memory architecture, promotion rules, rules directory patterns
- 2 templates: rule template, skill template
- 20 files, 1,829 lines

Integrates natively with Claude Code's auto-memory (v2.1.32+).
Reads from ~/.claude/projects/<path>/memory/ — no duplicate storage.
Promotes proven patterns from MEMORY.md to CLAUDE.md or .claude/rules/.

Also:
- Added to marketplace.json (18 plugins total)
- Added to README (Skills Overview + install section)
- Updated badge count to 88+
- Regenerated .codex/skills-index.json + symlink

Co-authored-by: Leo <leo@openclaw.ai>

engineering-team/self-improving-agent/.claude-plugin/plugin.json

@@ -0,0 +1,67 @@
+{
+  "name": "si",
+  "version": "1.0.0",
+  "displayName": "Self-Improving Agent",
+  "description": "Curate auto-memory, promote learnings to CLAUDE.md and rules, extract proven patterns into reusable skills.",
+  "skills": [
+    {
+      "name": "review",
+      "path": "skills/review",
+      "command": "/si:review",
+      "description": "Analyze auto-memory for promotion candidates, stale entries, and health"
+    },
+    {
+      "name": "promote",
+      "path": "skills/promote",
+      "command": "/si:promote",
+      "description": "Elevate a proven pattern from MEMORY.md to CLAUDE.md or .claude/rules/"
+    },
+    {
+      "name": "extract",
+      "path": "skills/extract",
+      "command": "/si:extract",
+      "description": "Turn a recurring pattern into a standalone reusable skill"
+    },
+    {
+      "name": "status",
+      "path": "skills/status",
+      "command": "/si:status",
+      "description": "Memory health dashboard with line counts, topic files, and recommendations"
+    },
+    {
+      "name": "remember",
+      "path": "skills/remember",
+      "command": "/si:remember",
+      "description": "Explicitly save important knowledge to auto-memory with context"
+    }
+  ],
+  "agents": [
+    {
+      "name": "memory-analyst",
+      "path": "agents/memory-analyst.md"
+    },
+    {
+      "name": "skill-extractor",
+      "path": "agents/skill-extractor.md"
+    }
+  ],
+  "hooks": {
+    "PostToolUse": [
+      {
+        "matcher": "Bash",
+        "hooks": [
+          {
+            "type": "command",
+            "command": "./hooks/error-capture.sh"
+          }
+        ]
+      }
+    ]
+  },
+  "settings": {
+    "memoryDir": "~/.claude/projects",
+    "maxMemoryLines": 200,
+    "promotionThreshold": 3,
+    "promotionWindowDays": 30
+  }
+}