feat(astrolabe): add Nextcloud PHP app for MCP server management

Adds a native Nextcloud app "Astroglobe" that provides:
- Personal settings: OAuth authorization for background MCP access
- Admin settings: Server status and vector sync monitoring
- API endpoints for MCP server communication

The app uses PKCE OAuth flow to obtain tokens for the MCP server,
enabling features like background vector sync per ADR-018.

Includes:
- PHP app structure (controllers, services, settings)
- Vue.js frontend components
- Docker compose mount configuration
- Installation hook for development testing
- ADR-018 documentation

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

third_party/astroglobe/templates/index.php

@@ -0,0 +1,11 @@
+<?php
+
+declare(strict_types=1);
+
+use OCP\Util;
+
+Util::addScript(OCA\Astroglobe\AppInfo\Application::APP_ID, OCA\Astroglobe\AppInfo\Application::APP_ID . '-main');
+
+?>
+
+<div id="astroglobe"></div>