feat(wiki): accent color + favicon (#0050)

Set the blue Docusaurus-style accent (#2b6cb0 light / #63b3ed dark) via injectCSS
on the app UI — the login page is excluded because Wiki.js renders it without
custom CSS, so a dark login card is not themeable and is left as-is. Mount the
ThreadNet favicon (favicon.ico + favicon-16/32 PNGs the browser tab uses) from the
platform-branding ConfigMap via subPath, overlaying only those files.

apps/production/wikijs.yaml

@@ -66,6 +66,21 @@ spec:
             - name: branding
               mountPath: /wiki/assets/img/branding
               readOnly: true
+            # Favicon (#0050): serve-favicon liest /wiki/assets/favicon.ico; der
+            # Browser-Tab nutzt zusätzlich die PNGs unter /_assets/favicons/. Einzelne
+            # Dateien per subPath überlagern, ohne die restlichen Default-Favicons zu verdecken.
+            - name: branding
+              mountPath: /wiki/assets/favicon.ico
+              subPath: favicon.ico
+              readOnly: true
+            - name: branding
+              mountPath: /wiki/assets/favicons/favicon-32x32.png
+              subPath: favicon-32x32.png
+              readOnly: true
+            - name: branding
+              mountPath: /wiki/assets/favicons/favicon-16x16.png
+              subPath: favicon-16x16.png
+              readOnly: true
           readinessProbe:
             tcpSocket:
               port: http