fix(build): sync VERSION file with semantic-release tags and add build time

- Update generate_build_metadata.sh to sync VERSION from latest git tag
- Change BUILD_DATE format from date-only to ISO 8601 with time (YYYY-MM-DDTHH:MM:SSZ)
- Fix VERSION file from 0.5.0 to 0.9.1 (matching latest git tag v0.9.1)
- Change version fallback from hardcoded '0.5.0-dev' to 'unknown' in config.py
- Update release.yml to commit all build metadata files (not just VERSION)
- Update BuildMetadata.md documentation to reflect automated versioning
- Add tests for build_date with time format and version unknown fallback

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>

app/config.py

@@ -284,7 +284,7 @@ class Settings(BaseSettings):
                 return f.read().strip()
 
         # Default version if not found
-        return "0.5.0-dev"
+        return "unknown"
 
     @property
     def git_sha(self) -> str: