Scale hidden line tolerance to model size and add optional full wireframe toggle

[dirlligafu]

Why?

Some models render with interior geometry visibly bleeding through the exterior ("x-ray" look, see #6) even though hidden-line removal is supposed to hide anything blocked from view. The actual cause isn't the model (normals, winding, etc. all checked out fine on the reported model). It's that the tolerance used to decide whether an edge is hidden behind a surface was a fixed absolute value, tuned for a "normal-size car" scale. Models exported at a very different unit scale (common for a lot of free/community downloads) end up with a tolerance larger than the entire model, so the occlusion test can never actually hide anything.

What was added / modified

• renderer.py: depth_eps now defaults to a value derived from the model's own size (half_span * 0.0075) instead of a fixed 0.018, so the occlusion test scales automatically with whatever unit scale a given model was exported at.
• Added an explicit "Show hidden lines (full wireframe, ignores what's blocked from view)" checkbox (Detail & Output section), for anyone who wants a full x-ray/wireframe render on purpose. Off by default, so the normal case is a clean render with no setup needed.
• app.py / templates/index.html: wired the new option through global preferences, request parsing, and the render call.

Testing

Reproduced the exact issue on the model from #6, confirmed the fix resolves it, and confirmed the new toggle reproduces the old full-wireframe look on demand when turned on. Also tested against several other models at normal scale to confirm no regression (huge X4 Foundations Carrier ships and small scout vessels models, all behaved as expected)

Closes #6

Preview

All lines hidden

All lines visible (none hidden)

Extra option in section 5 :