Sketch on the face you clicked, not the one you clicked twice

The previous commit made a picked face the sketch plane and I verified it
by clicking the face TWICE. That was the wrong test. handle_solid_click
cycles whole -> face -> edge, and "First click on a (new) body/face
selects the WHOLE solid; refine on repeat clicks" — so at level 1
m_sel_solid_face is -1, and one click on a face, which is what selecting
a face means to anyone, still fell through to the plane combo. The fix
was real and unreachable, which from the outside is indistinguishable
from no fix at all.

The face id was never missing. handle_solid_click resolves it by ray on
the FIRST click and passes it to on_solid_selection_changed regardless of
the cycle level; the panel simply discarded it whenever level < 2. Keep
it in m_pick_face/m_pick_face_body and let a sketch use it, preferring an
explicit face-level selection when there is one. Nothing about the cycle
changes, so body operations that rely on whole-body selection are
untouched.

The new state is dropped wherever the existing picks are, so a stale face
cannot come back: choosing a body from the Bodies list (an explicit
choice with nothing pointed at), picking a committed sketch loop (last
pick wins), undo/redo (recompute invalidates topology ids), and when a
sketch consumes the face.

Verified on :10 with ONE click, which is the flow that was broken: build
a box, single-click its top face, S then C, and the hint reads "Circle —
click center, then radius · on the picked face" with the circle drawn in
that face's plane (artifacts/shots/g3a2-01-one-click.png,
g3a2-02-sketch.png, g3a2-03-drawn.png).

GUI-only, so the kernel suite is unaffected — plane_of_face and its 154
cases / 2125 assertions are unchanged from the previous commit.

snaporca-3a2.

src/slic3r/GUI/DesignPanel.hpp

@@ -589,6 +589,12 @@ private:
     int               m_sel_solid_body{-1};   // which body the face/edge selection is on
     int               m_sel_solid_face{-1};
     int               m_sel_solid_edge{-1};
+    // The face actually under the last solid click, INDEPENDENT of the whole/face/edge cycle level.
+    // The first click on a solid selects the WHOLE body, but the ray has already resolved which face
+    // it hit and the callback passes it. "Sketch on the face I clicked" must not require discovering
+    // that a second click refines the selection, so keep it instead of throwing it away. snaporca-3a2.
+    int               m_pick_face_body{-1};
+    int               m_pick_face{-1};
     // What the live sketch was actually opened on ("the picked face", "XY", a datum's name), so the
     // hint can say it. Resolved from the selection at begin_sketch, not read back from a combo.
     wxString          m_sketch_on;