Add inventory management templates and utility functions

- Created HTML templates for inventory index, layout, search, settings, table, user, and worklog.
- Implemented utility functions for eager loading relationships in SQLAlchemy.
- Added validation mixin for form submissions.
- Updated project configuration files (pyproject.toml and setup.cfg) for package management.

setup.cfg

@@ -0,0 +1,9 @@
+[metadata]
+name = inventory
+version = 0.1.0
+
+[options]
+packages = find:
+
+[options.packages.find]
+where = .