feat: consolidated Gitea API client and pi extension

- Pure fetch-based API client (src/) with zero external dependencies
- Pi extension adapter (pi-extension/) registering 17 tools
- Standalone CLI (cli.ts) replacing gitea-scripts/gitea.js
- Token auth everywhere (no HMAC secrets)
- SKILL.md for agent auto-discovery
- TOOL.md with full parameter reference

Consolidates pi-bot/extensions/pi-gitea and clawbot/gitea-scripts
into a single shared package.

pi-extension/package.json

@@ -0,0 +1,9 @@
+{
+  "name": "pi-gitea",
+  "private": true,
+  "version": "1.0.0",
+  "type": "module",
+  "pi": {
+    "extensions": ["./index.ts"]
+  }
+}