chore: point repo/registry URLs at git.b1fr0st.eu (Forgejo->Gitea migration)

- Welcome.tsx REPO_URL (footer link) — takes effect on next image rebuild
- README clone URLs, docs/self-hosting.md image ref
- docker-compose.selfhost.yml image refs

docker-compose.selfhost.yml

@@ -30,7 +30,7 @@ services:
     restart: unless-stopped
 
   api:
-    image: forge.b1fr0st.eu/peter/siftlode:${IMAGE_TAG:-latest}
+    image: git.b1fr0st.eu/peter/siftlode:${IMAGE_TAG:-latest}
     env_file:
       - .env
     environment:
@@ -72,7 +72,7 @@ services:
   # DB (job queue) and the downloads mount with the API. Not read-only (yt-dlp/deno/ffmpeg write to
   # $HOME caches + the staging dir).
   worker:
-    image: forge.b1fr0st.eu/peter/siftlode:${IMAGE_TAG:-latest}
+    image: git.b1fr0st.eu/peter/siftlode:${IMAGE_TAG:-latest}
     command: ["python", "-m", "app.worker"]
     env_file:
       - .env