Add variable font weight axis support

[animeshbhuria]

Closes #50.
Adds a fontWeight property to TextStyle and a Weight slider in the text inspector's Typography section, applied via CoreText's wght variation axis in resolvedFont.
BundledFonts.swift already handled variable font registration correctly (dedups by family, per the existing comments) — the actual gap was downstream: the font picker and TextStyle only ever carried a font name, so nothing could select or apply a font's weight range even though it loaded correctly.
The slider is disabled (and visually dimmed) for fonts with no wght axis, detected via CTFontCopyVariationAxes — so static fonts like Poppins or Skia don't show a control that silently does nothing.
Scoped to static weight selection, addressing #50. Full animatable motion typography (keyframing weight/width over time) would be a separate, larger follow-up.
Tested locally and verified that: — confirmed the slider visibly changes rendered weight on bundled variable fonts (Geist, Inter, SpaceGrotesk, etc.), correctly stays disabled on static fonts (Poppins, Skia, Anton), and that existing saved project files without a fontWeight field still load correctly.

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Note

Low Risk
Localized text styling and rendering changes with safe fallbacks; minor layout risk from removing explicit word-wrap on paragraph style.

Overview
Adds fontWeight (default 400) to TextStyle with backward-compatible decoding, and a Weight scrubber in the text inspector Typography section that previews/commits through the existing text-style editor and refits clip bounds like font size.

Rendering now applies weight via CoreText’s wght variation axis in resolvedFont, with NaN/infinity clamping and a safe fallback when variation resolution fails. fontSupportsWeightAxis uses CTFontCopyVariationAxes so the slider is disabled and dimmed for fonts without a weight axis.

paragraphStyle no longer sets lineBreakMode to word wrapping. A small unit test covers fontWeight default and JSON round-trip.

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[davelab6]

Nice! Agreed that weight only is good to start; I suggest doing all axes for instance selection (so Kablammo or Recursive can pick a precis style desires) and tying optical size to font-size, as a middle step between this and motion typography.

Also STAT table support to select named styles from a drop-down, per axis, as demonstrated in lorp.github.io/samsa - would be another great waypoint.

Poppins and Skis are available as variable fonts btw

[animeshbhuria]

Thanks! Agreed all of those are good follow-ups — wanted to keep this PR scoped to just weight so it’s easy to review. Happy to look at STAT/named-instance support as a next PR if that’s useful direction-wise. Also noted re: Poppins/Skia — makes sense, the bundled files here are static, but good to know variable versions exist.

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