build: source from the unkin jellyfin-ha-src fork

Why:
- The build should pull from our own source fork so local HA patches can be
  carried and pinned, rather than cloning the upstream GitHub tree directly.

How:
- Point the clone URL in the Makefile and both Woodpecker pipelines at
  https://git.unkin.net/unkin/jellyfin-ha-src.git.
- Keep UPSTREAM_REF at d4f9c12c22d3a640f3b0a3622b23b8cd01d044ad, which is the
  seeded fork main, so the produced image is byte-identical for now; the
  feature bump is a later change.

.woodpecker/build.yaml

@@ -9,7 +9,7 @@ steps:
     commands:
       - |
         REF=$$(cat UPSTREAM_REF)
-        git clone https://github.com/ZoltyMat/jellyfin-ha.git src
+        git clone https://git.unkin.net/unkin/jellyfin-ha-src.git src
         git -C src checkout "$$REF"
         dotnet publish src/Jellyfin.Server/Jellyfin.Server.csproj \
           -c Release -r linux-x64 --self-contained false -o ./publish-output

.woodpecker/docker.yaml

@@ -9,7 +9,7 @@ steps:
     commands:
       - |
         REF=$$(cat UPSTREAM_REF)
-        git clone https://github.com/ZoltyMat/jellyfin-ha.git src
+        git clone https://git.unkin.net/unkin/jellyfin-ha-src.git src
         git -C src checkout "$$REF"
         dotnet publish src/Jellyfin.Server/Jellyfin.Server.csproj \
           -c Release -r linux-x64 --self-contained false -o ./publish-output