`try: from .x / except ImportError: from x` everywhere

[pmaasz]

128 occurrences across 43 files. This pattern is what you write when you're not sure whether the module is being imported as part of a package or as a top‑level script. The cost is:

• Every import does filesystem work twice.
• Genuine ImportErrors inside your own code are swallowed on the first try and get reported wrong on the second.
• Static analysis tools (pylint, mypy) go crazy.

Fix the packaging (you already have setup.py), run the app as python -m openlens, and delete all of them.

4.6 services.py is present but underused

src/services.py defines LensService / CalculationService / MaterialDatabaseService but most of its methods are bypassed:

• openlens.py:123 and the widget handlers mutate Lens directly and then call _save_to_database() on the main window.
• src/desensitization.py:156 and src/global_optimizer.py:119,219 call optimize_simplex(...) directly despite AGENTS.md stating "always use optimize()".

Either delete the service layer or actually route work through it. Right now it is a stub that future readers assume is real.