improve: apply Practical Typography guidelines to frontend

[cristipufu]

Summary

• Apply Butterick's Practical Typography guidelines across all frontend components
• Bump chat message/input text to 14px (guideline: 15–25px for web body text)
• Add proper line spacing (leading-normal/leading-relaxed) to all text-heavy panels
• Cap prose line length at ~65ch on chat messages and error details
• Soften dark-mode text-primary from #f1f5f9 to #cbd5e1 for reduced eye strain
• Add tracking-wider letterspacing to all uppercase text (guideline: 5–12% extra)
• Bump undersized text across NewRunPanel, SetupView, Sidebar, and graph controls
• Version bump 0.0.45 → 0.0.46

Test plan

• Verify chat messages render at 14px with proper line spacing
• Verify dark mode text is softer but still readable
• Verify all uppercase labels have visible letterspacing
• Verify log panel, trace tree, and span details have comfortable line height
• Verify NewRunPanel cards and SetupView empty state text are legible
• Check light mode is unaffected (only dark-mode text-primary changed)

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