refactor: consolidate version extraction logic and update workflow validation

Extracted version extraction logic from workflows into a centralized script for better reusability and consistency. Updated validation output naming for clarity.

Changes:
- Add extract_version.sh for centralized version extraction
- Remove update_version.sh (functionality integrated into workflows)
- Update validate_semver.sh output: release_type → is_prerelease
- Refactor docker-release.yml to use extract_version.sh
- Refactor github-release.yml to use centralized scripts
- Add version duplication check in version-release.yml

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

.github/scripts/validate_semver.sh

@@ -62,9 +62,9 @@ if [ -n "${GITHUB_OUTPUT:-}" ]; then
     echo "version=$VERSION" >> "$GITHUB_OUTPUT"
 
     if echo "$VERSION" | grep -q '-'; then
-        echo "release_type=prerelease" >> "$GITHUB_OUTPUT"
+        echo "is_prerelease=true" >> "$GITHUB_OUTPUT"
     else
-        echo "release_type=stable" >> "$GITHUB_OUTPUT"
+        echo "is_prerelease=false" >> "$GITHUB_OUTPUT"
     fi
 fi