feat: align select and pen gestures with standard outline editing

[kostyafarber]

Summary

• Select: dragging any unselected object inside the selection's bounding box now moves the whole selection instead of selecting the object under the pointer. Alt-drag keeps its own point-slide and duplicate behavior.
• Select: Shift-hover shows the add cursor over unselected points, anchors, segments, and components, matching what Shift-click adds.
• Select: the marquee selects a segment it touches unless exactly one of its end points is inside, so boxing a single point still selects only that point. Adds Curve.intersectsRect to @shift/geo.
• Pen: dragging from the active endpoint, or from an open end when no stroke is active, pulls the next segment's first handle. From a line the handle is free and the point stays a corner; Option keeps it on the line's direction and makes the point smooth. From a curve the incoming handle mirrors it. The pending handle stays drawn and shapes the next dragged curve; a click still draws a line.
• Pen: Escape during a closing drag now cancels the closing curve instead of leaving the contour closed with its preview handles.

Issue

Closes #465
Refs #369

Testing

• pnpm check passed.
• pnpm typecheck and pnpm lint:check passed.
• npx vitest run in apps/desktop: 1166 tests passed, including new regression tests in SelectMove.test.ts, Select.test.ts, and Pen.test.ts.
• npx vitest run in packages/geo: passed, including new Curve.intersectsRect tests.
• Manual: gestures checked in the running app during development.
• Desktop E2E runs on this pull request, not locally. The first run failed three canvas goldens in glyph-rendering.spec.ts (pen-cubic-curve, pen-s-curve-handles, pen-smooth-junction-drag-preview). Each diff is only the newly drawn pending handle: from the last point between gestures, and from the start of the curve being dragged. The baselines were replaced with the CI-rendered images after inspecting every diff.
• No screenshots attached: the changes are gesture behavior and a transient handle overlay.

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