docs: restructure repo — extract tools file, add CLAUDE.md, date-based versioning

- Move ECC setup guide reference from README to claude-code-tools.md
- Add CLAUDE.md with mandatory README sync rule
- Add "Last updated" date to README
- README is now a clean index of repo contents

claude-code-tools.md

@@ -0,0 +1,40 @@
+# Claude Code Tools & Extensions
+
+Useful tools, plugins, and extensions for Claude Code.
+
+## MCP Servers
+
+MCP (Model Context Protocol) servers are external processes that provide tools to Claude Code via a standardized protocol. They run alongside your session and extend Claude's capabilities.
+
+### Context7
+
+Up-to-date documentation and code examples for any library, available directly in your Claude Code session.
+
+- **Website:** <https://context7.com/>
+- **Setup:**
+
+  ```bash
+  claude mcp add --scope user --transport http context7 https://mcp.context7.com/mcp --header "CONTEXT7_API_KEY: <YOUR_API_KEY>"
+  ```
+
+- **Note:** API key can be created for free after signing in at [context7.com](https://context7.com/)
+
+## Skills (Slash Commands)
+
+Skills are a different extension mechanism from MCPs. They are prompt-based extensions invoked via `/skill-name` commands directly within Claude Code — no external server required.
+
+### AST Index
+
+Fast code search skill for Claude Code — find classes, symbols, usages, implementations, and more across large codebases using AST parsing.
+
+- **Repository:** <https://github.com/defendend/Claude-ast-index-search>
+- **Usage:** Invoke with `/ast-index` or related commands like "find class", "search for symbol", etc.
+
+## Toolkits
+
+### Everything Claude Code (ECC)
+
+A comprehensive collection of skills, rules, agents, and hooks for Claude Code.
+
+- **Repository:** <https://github.com/affaan-m/everything-claude-code>
+- **Setup guide:** [ecc-setup-guide.md](ecc-setup-guide.md)