Place and edit proof text as scene nodes

[kostyafarber]

Problem

Proof text cannot currently be placed and edited as a canvas object. The existing text interaction is tied to the glyph editor rather than an independently positioned run, which prevents a basic T → click → type workflow.

Expected outcome

A designer can place a text run in the scene, type and edit its content through a native input, and see the result update as the font or design-space location changes.

Acceptance criteria

• T and the Text toolbar button activate placement; a canvas click creates a text node with a focused caret.
• Typing, line breaks, deletion, arrows, selection, paste, and Escape work on the placed run; hover and scaled bounds/hits follow its rendered glyphs.
• Undo/redo restore text edits and the caret; exiting an empty run removes its node and undo restores it without reopening editing.
• Text nodes survive navigation between glyphs, and glyph/axis updates refresh the rendered run.
• Obsolete glyph-context text interaction is removed without losing its still-relevant behavioral coverage.

This covers the first interactive slice. Persistence, shaping, and proof-sheet workflows remain part of #113, not acceptance criteria here.