feat(theme-studio): replace the style toggles with weight/slant/underline/strike controls

The B/I/U/S toggle buttons in the syntax, UI, and package tables become a weight selector (light/normal/medium/semibold/bold/heavy), a slant selector (normal/italic/oblique), and box-like underline and strike controls. The underline control sets line or wave plus a color, and the strike control sets a color. A face can now reach the full weight range and a wavy or colored underline, not just bold and italic on-off.

All four controls come from one mkStyleControls helper shared across the three tables, and underline and strike share mkLineStyleControl (the box-control pattern, parameterized for a styled line vs a plain toggle). With the real controls in place I dropped the transitional legacyStyleOn/toggleLegacyStyle shim and its tests.

The overflow attributes (distant-fg, family, overline, inverse, extend, and inherit/height for ui and syntax) move into a per-row expander next.

Verified by screenshot and the browser style gate, which now drives a weight-select change and an underline-wave click through the model. Full suite green: Python 59, Node 198, ERT 41, plus the browser hash gates.

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