feat(ui): Select Other — pick what lies under something else (#503)

Hold the left button still (long-press on touch) or right-click › Select Other… to list everything under the cursor: sketch points and curves ("Line 3", "Point (arc 2 centre)"), vertices, edges, faces, bodies, profiles, planes and axes, filtered like a click and by the open dialog's active input. Hovering a row lights it up; clicking selects it (Shift/Ctrl add) or feeds the dialog. A repeat click on the same spot with nothing changed selects the next thing there; a double-click keeps its own actions.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/ui-egui/tests/scenarios/select_other_coincident_lines.json

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+[
+  {"note": "Two lines drawn on top of each other: holding the button still lists both, and the one underneath can be picked."},
+  {"start": "sketch.create"},
+  {"click": {"plane": "XY"}},
+  {"call": "ui.set", "params": {"showOrigin": false}},
+  {"call": "engine.execute", "params": {"command": "sketch.line", "params": {"points": [[0, 10], [20, 10]], "infer": false, "connect": false}}},
+  {"call": "engine.execute", "params": {"command": "sketch.line", "params": {"points": [[0, 10], [20, 10]], "infer": false, "connect": false}}},
+  {"hold": {"sketch": [10, 10]}},
+  {"expect": {"selection": 0, "sketching": true}},
+  {"move": {"handle": "select_other:1"}},
+  {"click": {"handle": "select_other:1"}},
+  {"expect": {"selection": 1}},
+  {"call": "ui.selectOther", "params": {"pick": 0}, "fail": true},
+  {"note": "Click cycling: a second deliberate click on the same spot selects the next line."},
+  {"click": {"sketch": [10, 10]}},
+  {"expect": {"selection": 1}}
+]