chore(ci): Adds nightly and release build workflows

- Introduces workflows for nightly and release builds,
  automating package publishing to Gitea.
- Includes scripts for setting Poetry version, cleaning up
  old dev versions, and uploading assets to releases.
- Adds a merge template for pull requests.

.gitea/scripts/get-release-id.sh

@@ -0,0 +1,21 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+# Eingaben
+TAG="$1"
+TOKEN="${ACTIONS_RUNTIME_TOKEN:-<fallback_token>}"
+REPO="${GITHUB_REPOSITORY:-owner/example}"
+API="${GITHUB_API_URL:-https://gitea.example.tld/api/v1}"
+
+OWNER=$(echo "$REPO" | cut -d/ -f1)
+NAME=$(echo "$REPO" | cut -d/ -f2)
+
+RESPONSE=$(curl -sf \
+  -H "Authorization: token $TOKEN" \
+  "$API/repos/$OWNER/$NAME/releases/tags/$TAG")
+
+RELEASE_ID=$(echo "$RESPONSE" | jq -r '.id')
+echo "Release-ID für $TAG ist: $RELEASE_ID"
+
+# Für GitHub Actions als Umgebungsvariable
+echo "GT_RELEASE_ID=$RELEASE_ID" >> "$GITHUB_ENV"