feat: fillet fit option reduces a radius too large for its edges (#388)

* feat(kernel): typed TooLarge refusal and fillet_max search

Blend refusals caused only by the size (larger than the neighbouring faces,
taller than the walls, longer than the next edge, larger than a corner
radius) now return KernelError::TooLarge, displayed as before. fillet_max
finds the largest radius below a request at which the fillet of the edges
works, to three significant digits, by building candidates; it is an explicit
call (up to 16 fillets), not run on every refusal.

A corner edge that doesn't run square to the edge is now reported as such
instead of as a blend larger than the neighbouring faces.

Refs #293

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TWc1smHYwTSVrVc8SNvS44

* feat: fillet fit option reduces a radius too large for its edges

solid.fillet takes fit: exact (the default, as before: a radius too large
for the geometry around the edges is refused) or reduce: the radius is
reduced to the largest that works for all the picked edges (kernel
fillet_max, three significant digits, every candidate built). The feature
stores the requested radius, so it refits on every evaluation; when it
reduces, the feature's warning says so and the command returns
radius_applied. Pattern copies of the fillet use the same rule. The file
format writes fit only when it is reduce.

The Fillet dialog gets a Radius Fit row (Exact / Reduce to Fit, constant
radius) and, when the preview reduced the radius, an Applied Radius line;
editing the feature keeps the choice.

One radius for all edges for now; per-edge radii and taper follow.

Refs #293

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TWc1smHYwTSVrVc8SNvS44

---------

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
Co-authored-by: bherbruck <brennen.herbruck@gmail.com>

crates/kernel/src/curveblend.rs

@@ -691,7 +691,7 @@ fn curve_blend_with_limit(solid: &Solid, ids: &[mt::EdgeID], size: f64, r: f64,
             let (ta, oa) = a.as_ref().map(at).unwrap_or((0.0, 0.0));
             let (tb, ob) = b.as_ref().map(at).unwrap_or((1.0, 0.0));
             if oa > size * 1e-5 || ob > size * 1e-5 || ta < -1e-9 || tb > 1.0 + 1e-9 || tb - ta < 1e-6 {
-                return Err(unsupported("the blend is larger than the neighbouring faces"));
+                return Err(crate::blend::too_large("the blend is larger than the neighbouring faces"));
             }
             let a = a.unwrap_or_else(|| seam.front().clone());
             let b = b.unwrap_or_else(|| seam.back().clone());