docs: adopt semantic versioning — release 1.27.1 tracks Gitea 1.27.1

Templates were re-checked against the local gitea clone (v1.27.1 tag): all
46 translation keys exist in locale_en-US, all data paths match the official
templates, and all 110 templates render via `go run . preview all` — no
template changes required.

From now on release versions mirror the Gitea version they support:
- COMPATIBILITY.md: quick reference now leads with release 1.27.1
  (max tested Gitea 1.27.1, active), v1.0.x marked superseded; new
  Versioning section documents the scheme
- README: release version in header + versioning bullet
- Tracker workflow PR body: added semantic-versioning release checklist
  (bump Template Release column, tag vX.Y.Z)

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

.github/workflows/gitea-tracker.yml

@@ -126,6 +126,11 @@ jobs:
             - [ ] Run `cd tools && go run . preview all` to confirm templates still render
             - [ ] Update status from ⏳ to ✅ (compatible) or ❌ (breaking) in COMPATIBILITY.md
             - [ ] Update the `Mail Template Changes` and `Breaking?` columns with accurate notes
+
+            ## Release (semantic versioning)
+            Once verified, releases mirror the Gitea version:
+            - [ ] Bump the **Template Release** column in `COMPATIBILITY.md` to **${{ steps.version.outputs.new_version }}**
+            - [ ] Tag the release with the same number: `git tag v${{ steps.version.outputs.new_version }} && git push origin v${{ steps.version.outputs.new_version }}` — the release workflow packages the archive automatically
           labels: compatibility, automated
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}