frontend/ci: Getrennte Footer-Links — Name -> Repo, Version -> Commit

Im Footer sind "Werkbaum" und die Versionsnummer jetzt zwei Links:
- "Werkbaum" -> Repo-Startseite (wie bisher).
- Versionsnummer (<a class="ver">) -> exakt der deployte Commit.

CI setzt beim Build sowohl den Versionstext als auch den href der
ver-Anchor: COMMIT_URL=.../commit/$(git rev-parse HEAD); zwei gezielte
seds (href + Text). Lokal zeigt die Version "1.0" und verlinkt die
Commits-Uebersicht als Fallback.

Verifiziert: YAML gueltig; Trockenlauf ersetzt href -> commit/<sha> und
Text -> 1.0.7, "Werkbaum"-Link unveraendert. Preview lokal: Name -> Repo,
Version -> /commits/main.

Doku: README (EN+DE) Deployment + DECISIONS D16 ergaenzt.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

README.md

@@ -67,8 +67,10 @@ While assembling the site, the workflow also stamps the version into the footer:
 commit"), and the **micro** part is the number of commits since that last bump —
 so it grows with every commit and resets to `0` right after a bump
 (`Werkbaum 1.0.0`, `1.0.1`, … then bump `VERSION` to `1.1` → `1.1.0`). Nothing is
-written back to the repo. Opened locally, the editor shows the source
-placeholder (`Werkbaum 1.0`).
+written back to the repo. In the footer the name **Werkbaum** links to the
+repository, while the **version number** links to that exact commit
+(`…/commit/<sha>`). Opened locally, the editor shows the source placeholder
+(`Werkbaum 1.0`).
 
 **One-time setup:** In the repo settings under **Pages**, select **Source** =
 "GitHub Actions". The repo must be **public** for this (GitHub Pages via Actions