Alias navigation preset uses Shift+Alt with LMB/MMB/RMB (Fixes #304) (#306)

Navigation presets are now a table of bindings (button, required modifier
keys, camera mode) instead of string matches. The Alias preset binds
Shift+Alt+left to orbit, Shift+Alt+middle to pan and Shift+Alt+right to
zoom. A left press with a binding's keys is latched until release, so that
drag neither box-selects nor drags sketch geometry; plain left drags behave
as before. Shift only requests snapping when the binding without Shift
still orbits.

The scenario harness sends Alt with ui.drag/ui.click, and camera checks can
assert panned/zoomed since the last camera step. The user guide notes Alt+drag
grabs by KDE and GNOME and how to free them.


Claude-Session: https://claude.ai/code/session_01RjGw4gA5ZvKrU8MQP6sBgT

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

crates/ui-egui/src/control.rs

@@ -228,7 +228,7 @@ pub fn handle(app: &mut SolveApp, ctx: &egui::Context, req: &ControlRequest) ->
                     Some("middle") => egui::PointerButton::Middle,
                     _ => egui::PointerButton::Primary,
                 };
-                let modifiers = egui::Modifiers { shift: b("shift"), ctrl: b("ctrl"), command: b("ctrl"), ..Default::default() };
+                let modifiers = egui::Modifiers { shift: b("shift"), ctrl: b("ctrl"), command: b("ctrl"), alt: b("alt"), ..Default::default() };
                 // `double: true` sends two clicks in one frame, which egui reads as a double-click.
                 for _ in 0..if b("double") { 2 } else { 1 } {
                     app.synthetic.push(egui::Event::PointerButton { pos, button, pressed: true, modifiers });
@@ -244,7 +244,7 @@ pub fn handle(app: &mut SolveApp, ctx: &egui::Context, req: &ControlRequest) ->
                 Some("middle") => egui::PointerButton::Middle,
                 _ => egui::PointerButton::Primary,
             };
-            let modifiers = egui::Modifiers { shift: b("shift"), ctrl: b("ctrl"), command: b("ctrl"), ..Default::default() };
+            let modifiers = egui::Modifiers { shift: b("shift"), ctrl: b("ctrl"), command: b("ctrl"), alt: b("alt"), ..Default::default() };
             let (a, z) = (egui::pos2(x0 as f32, y0 as f32), egui::pos2(x1 as f32, y1 as f32));
             app.synthetic.push(egui::Event::PointerMoved(a));
             app.synthetic.push(egui::Event::PointerButton { pos: a, button, pressed: true, modifiers });