fix: CPU calc, disk card, lifespan, remove Google Fonts CDN, fix doc link

- Fix Docker container CPU % (multiply by num_cpus)
- Add missing Disk usage card to system status grid
- Replace deprecated @app.on_event with lifespan context manager
- Move `import requests` to module level
- Remove Google Fonts CDN dependency from CSS
- Update naming doc URL to real raw Gitea link

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

templates/index.html

@@ -63,6 +63,16 @@
                     </div>
                 </div>
 
+                <div class="stat-card">
+                    <div class="stat-label">Disk usage</div>
+                    <div class="stat-value" x-text="system.disk.percent + '%'"></div>
+                    <div class="progress-bar">
+                        <div class="progress-fill" :style="`width: ${system.disk.percent}%`"
+                            :class="getProgressColor(system.disk.percent)"></div>
+                    </div>
+                    <div class="stat-detail" x-text="`${system.disk.used_gb} GB / ${system.disk.total_gb} GB`"></div>
+                </div>
+
                 <div class="stat-card">
                     <div class="stat-label">Docker containers</div>
                     <div class="stat-value" x-text="`${system.containers.running} / ${system.containers.total}`"></div>