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/settings/error.php

@@ -0,0 +1,53 @@
+<?php
+/**
+ * Error template for MCP Server UI settings.
+ *
+ * Displayed when the MCP server cannot be reached or returns an error.
+ *
+ * @var array $_ Template parameters
+ * @var string $_['error'] Error title
+ * @var string $_['details'] Error details/message
+ * @var string $_['server_url'] Configured server URL (optional)
+ * @var string $_['help_text'] Additional help text (optional)
+ */
+
+style('astroglobe', 'astroglobe-settings');
+?>
+
+<div class="mcp-settings-error">
+	<div class="notecard notecard-error">
+		<h3>
+			<span class="icon icon-error"></span>
+			<?php p($_['error'] ?? 'Error'); ?>
+		</h3>
+
+		<?php if (isset($_['details'])): ?>
+			<p><strong><?php p($l->t('Details:')); ?></strong></p>
+			<p><code><?php p($_['details']); ?></code></p>
+		<?php endif; ?>
+
+		<?php if (isset($_['server_url'])): ?>
+			<p><strong><?php p($l->t('Server URL:')); ?></strong></p>
+			<p><code><?php p($_['server_url']); ?></code></p>
+		<?php endif; ?>
+
+		<?php if (isset($_['help_text'])): ?>
+			<p class="mcp-help-text"><?php p($_['help_text']); ?></p>
+		<?php endif; ?>
+
+		<h4><?php p($l->t('Troubleshooting Steps:')); ?></h4>
+		<ol>
+			<li><?php p($l->t('Verify the MCP server is running and accessible')); ?></li>
+			<li><?php p($l->t('Check that mcp_server_url in config.php is correct')); ?></li>
+			<li><?php p($l->t('Ensure mcp_server_api_key matches the server configuration')); ?></li>
+			<li><?php p($l->t('Check firewall rules and network connectivity')); ?></li>
+			<li><?php p($l->t('Review MCP server logs for errors')); ?></li>
+		</ol>
+
+		<p>
+			<a href="https://github.com/cbcoutinho/nextcloud-mcp-server/blob/master/docs/ADR-018-nextcloud-php-app-for-settings-ui.md" target="_blank" class="button">
+				<?php p($l->t('View Documentation')); ?>
+			</a>
+		</p>
+	</div>
+</div>