Introduce opendataloader and PaddleOCR-VL parser engines with tenant-level
settings UI, replace liteparse, and harden Excel/PPT/Markdown parsing.
Optional odl-hybrid sidecar stays local-build only and is excluded from
default dev-start and full profiles.
- Add docstrings and inline comments for key functions and complex logic
- Unify comment style, eliminate magic numbers and ambiguous variable names
- No functional changes, only improve maintainability