feat: multiline text with word-wrapping and leading control

[eugenioenko]

Summary

• Replace Two.Text with twojs-multiline-text library for proper multiline rendering
• Hard line breaks: Shift+Enter in the text overlay creates \n breaks that render correctly
• Word-wrapping: Drag-to-create text boxes wrap text at the boundary via the library's width property
• Leading control: New slider in text toolbar (0.8–3.0) and properties panel for selected text
• Backward compatible — old single-line text loads with default leading (1.3)

Known issue

Minor vertical text shift (~2-8px depending on font size) on commit — pre-existing issue caused by CSS vs SVG baseline model differences, not a regression from this change.

Test plan

• Click canvas → type single-line → renders correctly
• Click canvas → Shift+Enter → multiline renders with line breaks
• Drag a text box → type long text → word-wraps at boundary
• Change leading in toolbar → new text uses updated leading
• Select text → change leading in properties panel → text re-renders
• Reload page → persisted text loads correctly (including multiline)
• Old single-line text from before the change still loads fine

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