Fix mobile browser theme color, sidebar and RecFlow

[zhangzhenghao]

Summary

• Add a theme-color meta tag so mobile Chrome can tint the address bar
• Update the meta color when the dashboard theme is applied or toggled
• Initialize the meta color before app boot based on stored/system theme

Test Plan

• pnpm install --frozen-lockfile
• pnpm lint
• pnpm test --runInBand
• git diff --check

Note: pnpm build completed the legacy bundle but timed out twice while starting the module bundle in this environment; the partial build only emitted existing Sass deprecation and asset-size warnings before timeout.