Dark-only: no light theme / prefers-color-scheme support

[aasis21]

↻ Code moved — RTK refactor (#143). The mobile app was restructured into CORE (session/) / EDGE (session/runtime/ + services/) / SHELL (ui/ + app/). Behavior was preserved, so this finding still applies; line numbers in the body below are pre-refactor. Updated pointers:

• chat.css → mobile/src/ui/styles/chat.css
• styles.css → mobile/src/ui/styles/styles.css

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Problem

color-scheme: dark is hardcoded and the palette is fixed (GitHub dark tokens in chat.css, ink/blue tokens in styles.css). There's no light theme or prefers-color-scheme handling — bad for outdoor phone readability and users who prefer light.

Suggested fix

Introduce theme tokens with a light variant and honor prefers-color-scheme (plus an in-app toggle).

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Filed from a UI research sweep of the Helm mobile app (landing + live demo session) using Playwright + full source review, cross-referenced against Claude, ChatGPT, GitHub Copilot Chat, and Codex/Claude Code UIs.

[aasis21]

Fixed in b3e86c1. chat.css/styles.css color tokens gained light values via @media (prefers-color-scheme: light) plus explicit :root[data-theme='light'|'dark'] overrides; the Settings Theme control (System/Light/Dark) sets document.documentElement.dataset.theme, so system preference is honored by default with an in-app override.