feat(web): logs and troubleshooting screens for SPA parity (#145)

Add typed API wrappers (api/logs.ts, api/troubleshoot.ts) and two new
screens: LogsScreen (paged, level-badged, server-side filtered log table)
and TroubleshootingScreen (General JSON viewer with copy, plus per-platform
NVIDIA/QSV/VAAPI/VideoToolbox capability tabs when populated). Both are
registered under a new "System" nav group in App.tsx alongside Settings.
Settings' Classic UI help text and About card now point at the new screens
instead of the Blazor logs/troubleshooting pages.

web/src/shell.css

@@ -3316,6 +3316,20 @@
   color: var(--text-secondary);
 }
 
+.ctv-troubleshoot-pre {
+  max-height: 60vh;
+  overflow: auto;
+  margin: 0;
+  padding: 12px;
+  border-radius: var(--radius-sm);
+  background: var(--ctv-surface-2);
+  border: 1px solid var(--border-hairline);
+  font: var(--text-xs) / 1.5 var(--font-mono);
+  color: var(--text-secondary);
+  white-space: pre-wrap;
+  word-break: break-word;
+}
+
 .ctv-settings-flush-row {
   display: flex;
   align-items: center;