Adopt the M3 type scale on self-hosted Roboto Flex

[danielchalmers]

Summary

Closes out the typography item of the MD3E makeover:

• Self-hosted Roboto Flex: the variable font (weight axis 100-1000) ships as latin + latin-ext woff2 subsets, 57KB total, declared with proper unicode-range so other scripts fall back to system Roboto. The app's text no longer depends on whatever the WebView provides.
• Full M3 type scale in the theme: display (H1-H3), headline (H4-H6), title (Subtitle1/2), body (Body1/2), and label (Button/Caption/Overline) roles with M3 sizes, weights, line heights, and letter spacing, replacing MudBlazor's stock M2 scale. Buttons and labels move to 500 weight with label-large tracking; body text gets the M3 tracking values.
• Removed the now-redundant dialog headline CSS patch, since h6 natively renders as headline-small (24px regular). The app bar title-large override stays, since that's a deliberate role remap for toolbars.
• Caption keeps its intentional line-height 1 for the compact calendar and chart labels.

Test plan

• dotnet test -f net10.0 (236 passed, including the palette parity suite against the restructured theme builder)
• Verified on the API 35 emulator via Chrome DevTools Protocol that document.fonts.check('16px "Roboto Flex"') is true, the computed body font stack leads with Roboto Flex, and body-medium metrics (14px, 1.43 line height, 0.25px tracking) plus 500-weight labels are applied.
• Before/after screenshots (Home light/dark, Settings light) incoming below.

[danielchalmers]

Not necessary since we only deploy to Android which has Roboto