fix(bump): Schutz vor Doppel-Tags nur für Tags derselben Art (#5)

Der Schutz „Commit trägt schon ein v-Tag, nichts tun“ zählt jetzt nur Tags derselben Art (dev, beta, stabil). Vorher hätte ein dev-Tag nach einem Fast-Forward-Merge in `release/*` das Beta-Tag und damit Build und Deploy nach beta verhindert.

Getestet im lokalen Harness: Feature vom Release-Head taggen, Fast-Forward nach `release/2.4`, Lauf auf release ergibt `v2.4.1-beta.2` auf demselben Commit; erneuter Lauf tut nichts. Release als `bump-v2.0.1`.

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Reviewed-on: #5

README.md

@@ -182,7 +182,7 @@ Derives the next version for the pushed branch and pushes it as a tag on the tri
 
 If the stable tag of a line exists (`v2.4.0` after the release), the next patch of that line is used (`v2.4.1-beta.0`, `v2.4.1-dev.…`).
 
-Only the commit that triggered the pipeline is tagged; if the branch moved on, the step exits without a tag and the newer pipeline takes over. A commit that already carries a `v*` tag is not tagged again, so a re-run does not build twice.
+Only the commit that triggered the pipeline is tagged; if the branch moved on, the step exits without a tag and the newer pipeline takes over. A commit that already carries a tag of the same kind (dev, beta or stable) is not tagged again, so a re-run does not build twice; a dev tag does not block the beta tag after a fast-forward merge.
 
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