mesh-compile: sweep along an elevated directrix (Elevated3) with a certified deviation

[GeneralPawz]

Reported by a consumer (axioval), seen in axiolid-mesh-compile 0.3.10–0.3.12. The reference mesh compiler can't sweep along an elevated directrix (`Curve3::Elevated`, which a gradient curve lowers to): it returns `GeomError::Unsupported { operation: CurveEvaluation }`, even for a constant grade. `evaluate3` has no `Elevated` arm (noted as open in #239), and sweep directrix resolution classifies elevated curves as an unsupported family. Example: a pipe whose swept disk follows a gradient curve with a vertical circular sag (R = 1000) is unmeasured.

The building blocks exist: `elevated_point`/`elevated_tangent` (#238 `elevation_height`/`elevation_grade`, #239 chains as plans), `elevation_chord_bound` (#238), the plan's chord bounds (#232/#239), and the banked section frames (#240).

Proposal

• Add `Curve3::Elevated` to `evaluate3`/`derivative3`/`domain3`.
• Accept elevated (and banked) directrices for swept disks and swept areas. Sample the directrix by plan distance with a certified 3D chord bound composed from the plan's bound and the elevation's `elevation_chord_bound`; plan and elevation chord errors combine, so derive the 3D bound and split the budget. Sweep with frames along the 3D tangent; for `Banked3`, use its section frames.
• Report the deviation as `Certified`/`Proven` through `compile_mesh_with_deviation`, or as `Unbounded` by name where a piece can't be bounded.

Done when

• A swept disk and a swept area along `Elevated3` directrices with line, circular-arc (curve: exact vertical circular-arc and clothoid elevation laws #238) and parabolic vertical profiles, over straight, arc and clothoid plans, compile to watertight meshes.
• Dense sampling stays within the reported certified deviation.
• Volume matches the closed form for a straight plan with a constant grade.
• A banked directrix sweeps with the rolled frames.

[GeneralPawz]

Released in axiolid-construct 0.3.15, axiolid-evaluate 0.3.6, axiolid-reference 0.3.7, axiolid-mesh-compile 0.3.14 (9877cdc).