fix(ui): improve readability and accessibility

[luispabon]

Summary

Fixes #60.

• Increase the shared type scale and chart labels/tooltips while keeping the default interface geometry at 100%, avoiding CSS zoom as the readability mechanism.
• Raise secondary text contrast, darken the neutral surface palette, and give interactive control boundaries and deep-sleep graphics at least 3:1 contrast.
• Add symbols or patterns to good/bad/flat states so colour is not the only cue.
• Widen the sidebar and weekly report layout for the larger text, and stop the training threshold chart clipping its bpm labels.
• Update the bilingual changelog and UI design guidance to match the final tokens.

Accessibility details

• Body text: 13px to 16.5px.
• Small text: former 8–11px roles now use 11–14.5px.
• The previous faint grey tier, measured at about 2.0:1, now aliases the passing subtle tier.
• Interactive boundaries use a separate high-contrast token instead of making every decorative divider prominent.
• Deep-sleep blue was raised from 2.59:1 to above 3:1 on its chart surfaces.
• Delta states use ✓, !, or =; negative bars also use a stripe pattern.

Before

After

[lingcang728]

Thanks for improving that ！

[luispabon]

Thank you!