Fetch history and tags in the canonical workflow (closes #110)

The checkout step of the canonical `.gitea/workflows/check.yml` now sets `fetch-depth: 0`, with a one-line comment saying why. The checkout action otherwise clones shallow with no tags, so `git describe --tags --always` gave a bare short commit id in CI where a local build of a tagged repository gives the tag. `REPO_POLICIES.md` and the existing repo checklist told each tagged repository to add it itself, which a byte-identical re-vendor would remove; they now say the canonical file sets it.

Unverified: the live check, which waits on the shared runner.

Model: opus-5-5

TODO.md

@@ -21,6 +21,13 @@ fmt-check, and commit.
 
 # Completed Steps
 
+- 2026-10-06: The canonical `.gitea/workflows/check.yml` now sets
+  `fetch-depth: 0` on its checkout step (issue 110), so CI fetches the history
+  and tags that `git describe --tags --always` needs, and a tagged repository
+  stamps the same version in CI as in a local build. `REPO_POLICIES.md` and the
+  existing repo checklist now say the canonical file sets it, instead of asking
+  each repository to add it. Not yet tried on the shared runner, which is out of
+  disk space. Repositories pick this up on their next re-vendor.
 - 2026-10-06: The canonical `.gitea/workflows/check.yml` now has a `concurrency`
   block, so a new push cancels the older run on the same branch and no other,
   and its checkout step sets `persist-credentials: false`, so the job's token is