Revert the CI full-fetch workaround and drop unreachable workflows

Shallow clones were never a Gitea packing bug. An intruder had set
uploadpack.packObjectsHook in Gitea's HOME gitconfig, pointing at a
non-executable dropper, so every upload-pack died mid-pack. That hook is
gone and --depth=1 clones are verified working, so fetch-depth: 0 buys
nothing but slower CI. See INCIDENT-2026-08-11.md.

op25-container/.gitea/workflows/* never ran: Gitea only executes
workflows under .gitea/workflows at the repo root, and op25-container is
a subdirectory of this repo, not a repo of its own. The live OP25 image
build is .gitea/workflows/build-op25.yml.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

.gitea/workflows/build-icecast.yml

@@ -16,11 +16,7 @@ jobs:
     env:
       CONTAINER_NAME: icecast
     steps:
-      # Full fetch: Gitea fails to pack the default depth=1 shallow clone
-      # ("bad pack header"). Don't set this back to a shallow fetch.
       - uses: actions/checkout@v4
-        with:
-          fetch-depth: 0
 
       - uses: docker/setup-qemu-action@v3