feat: add React SettingsContext with useSettings and useTheme hooks

[devin-ai-integration]

Summary

Phase 1 of the Angular-to-React migration: converts the Angular SettingsService (src/app/shared/services/settings.service.ts) into a React Context (src/context/SettingsContext.tsx).

Adds:

• Settings interface and SettingsContextValue type
• SettingsProvider component with localStorage persistence for openLinkInNewTab, theme, titleFontSize, listSpacing
• System dark mode detection via window.matchMedia('(prefers-color-scheme: dark)') with a change event listener
• useSettings() hook — exposes all settings state + toggleSettings, toggleOpenLinksInNewTab, setTheme, setFont, setSpacing
• useTheme() hook — narrow accessor for theme + setTheme

Single file added, no existing files modified.

Local Testing

The existing Angular app compiles and runs successfully (ng serve) with the new file in place — no regressions to the current app.

Review & Testing Checklist for Human

• Verify behavioral parity with Angular service — compare initTheme() logic (lines 59–68 in new file) against the Angular version. When no saved theme exists, the React version reads matchMedia.matches synchronously rather than dispatching a synthetic event like Angular does — confirm this is acceptable.
• System dark mode listener overrides user-saved theme — the change listener (lines 71–80) calls setTheme unconditionally, which will overwrite a manually chosen theme if the OS preference flips. This matches the Angular behavior but may be undesirable long-term.
• Toggle callbacks use direct state reads — toggleSettings and toggleOpenLinksInNewTab read settings.showSettings / settings.openLinkInNewTab from closure rather than using a functional updater with prev. Dependency arrays look correct so it should work, but worth a second look for potential stale-closure edge cases under rapid toggling.
• No runtime tests — this was type-checked against @types/react@17 but there are no unit tests and no consumers yet (Phase 1). Plan to add tests and wire up the provider in a subsequent phase.

Suggested test plan: Once a later phase wires up SettingsProvider, manually toggle each setting in the UI, refresh the page, and confirm values persist via localStorage. Also toggle OS dark mode and verify the theme updates automatically.

Notes

• Requested by: @eashansinha
• Link to Devin run

[devin-ai-integration]

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