[raykholo]

Port of tangency-labs#7652 (contour flange options, by @plexi32) onto the surfaces-first develop in tangency-labs#9245.

What it does

• Radius override on a contour flange, instead of only the rule's bend radius.
• Orientation (side 1 / center / side 2) places the sheet's thickness against the drawn profile. On Sheet metal: one model, the part's surfaces; the flat pattern is derived (#6748) tangency-labs/solidcraft#9245 this becomes a depth into SurfaceSheet::contour: side 1 = 0, center = t/2, side 2 = t, with offset_profile shifting the sketch.
• A legacy reverse still works when no orientation is set.

Changes from the original

• The original drove the flat-to-3D bridge, which Sheet metal: one model, the part's surfaces; the flat pattern is derived (#6748) tangency-labs/solidcraft#9245 removes. The options now feed the surfaces directly (cfe406d, authored by Frank).
• New (7eaaee3): a sharp corner beside an arc used to stop with "not supported yet". It now meets where the shifted line and shifted circle (or two shifted circles) cross, and the arc takes a new start and sweep. Closed-form unit tests cover line/arc and arc/arc corners.
• The engine test for that profile pins the base's current refusal ("a bend on the edge of a roll") at all three orientations. Rolls are outside this PR.

Tests (buildq)

• engine contour_flange: 10 passed
• engine schema::sheet: 14 passed
• doc sharp-corner unit tests: 2 passed
• ui-egui contour_flange: 1 passed

Credit: @plexi32 (Frank) for the feature and the original PR.