[codex] add optional bundled fonts for theme and skia

[ola-893]

Summary

Adds optional bundled font support for the theme crate and cleans up the dormant Skia renderer path.

• Gates bundled theme font bytes behind the bundled-fonts feature
• Keeps bundled fonts enabled by default for compatibility
• Makes the Skia renderer fall back to a system typeface when bundled bytes are disabled
• Removes hardcoded 10000.0 text layout fallbacks in Skia
• Excludes the currently commented-out Skia crate from workspace membership so it can be checked directly by manifest
• Fixes Skia compile drift against the current fission-render Fill and Stroke types

Why

The theme crate embedded font assets unconditionally, and Skia had a large magic width fallback for unconstrained text. The Skia crate was also commented out of workspace members but not excluded, which prevented direct manifest checks.

Impact

Default consumers keep current bundled-font behavior. Consumers that disable default features can avoid embedding theme font bytes, while Skia can still construct a fallback typeface.

Validation

• cargo check -p fission-theme --locked --offline
• cargo check -p fission-theme --no-default-features --locked --offline
• cargo check -p fission-shell-winit --lib --locked
• cargo check --manifest-path crates/rendering/fission-render-skia/Cargo.toml