feat(ui): show build version in footer; enable watchtower for caddy

- Footer now displays build version tag + short commit SHA (from
  PUBLIC_BUILD_VERSION / PUBLIC_BUILD_COMMIT env vars baked in at
  image build time); falls back to 'dev' in local builds
- docker-compose.yml: add watchtower label to caddy service so it
  auto-updates alongside backend/ui/runner on new image pushes
- homelab/docker-compose.yml: use locally-built kokoro-fastapi:latest
  image (consistent with actual homelab setup)

docker-compose.yml

@@ -366,6 +366,8 @@ services:
     build:
       context: ./caddy
       dockerfile: Dockerfile
+    labels:
+      com.centurylinklabs.watchtower.enable: "true"
     restart: unless-stopped
     depends_on:
       backend:

homelab/docker-compose.yml

@@ -394,7 +394,7 @@ services:
   # Voices match existing IDs: af_bella, af_sky, af_heart, etc.
   # The runner reaches it at http://kokoro-fastapi:8880 via the Docker network.
   kokoro-fastapi:
-    image: ghcr.io/remsky/kokoro-fastapi-gpu:latest
+    image: kokoro-fastapi:latest
     restart: unless-stopped
     deploy:
       resources:

ui/src/routes/+layout.svelte

@@ -432,8 +432,18 @@
 			<a href="/privacy" class="hover:text-zinc-500 transition-colors">Privacy</a>
 			<a href="/dmca" class="hover:text-zinc-500 transition-colors">DMCA</a>
 			<span>&copy; {new Date().getFullYear()} libnovel</span>
+		</div>
+		<!-- Build version / commit SHA -->
+		<div class="text-zinc-700 tabular-nums font-mono">
 			{#if env.PUBLIC_BUILD_VERSION && env.PUBLIC_BUILD_VERSION !== 'dev'}
-					<span class="text-zinc-800">{env.PUBLIC_BUILD_VERSION}+{env.PUBLIC_BUILD_COMMIT?.slice(0, 7)}</span>
+				<span title="Build version">{env.PUBLIC_BUILD_VERSION}</span>
+				{#if env.PUBLIC_BUILD_COMMIT && env.PUBLIC_BUILD_COMMIT !== 'unknown'}
+					<span class="text-zinc-800 select-all" title="Commit SHA"
+						>+{env.PUBLIC_BUILD_COMMIT.slice(0, 7)}</span
+					>
+				{/if}
+			{:else}
+				<span class="text-zinc-800">dev</span>
 			{/if}
 		</div>
 		</div>