manifests: re-pin moving tags so Renovate can track them

- umami       postgresql-latest  -> postgresql-v1.38.0
  - filebrowser v2-alpine          -> v2.63.13

These two were "latest"-style moving tags that Renovate physically
cannot propose updates for. Pinning to current upstream versions so
future bumps go through the normal Renovate PR flow.

Note: Renovate operates from the homelab-manifests repo, not this one
yet — but felhom-system/* copies exist in homelab-manifests for
discoverability, and Renovate already tracks the pinned forms via a
new customManager for the umami `postgresql-vX.Y.Z` pattern (added in
homelab-manifests admin-system/renovate.yaml). For now, future bumps
will need to be applied to both repos until we consolidate the source
of truth.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

manifests/webpage.yaml

@@ -107,7 +107,7 @@ spec:
     spec:
       containers:
         - name: filebrowser
-          image: filebrowser/filebrowser:v2-alpine
+          image: filebrowser/filebrowser:v2.63.13
           ports:
             - containerPort: 8080
           volumeMounts: