Purpose

Centralize shared application state with Redux Toolkit so selected parts, authentication, and notifications stay consistent across pages and components.

Changes

• Replace build and authentication contexts with Redux slices and a shared store.
• Update part cards, detail views, and the PC builder to read and update selected parts through Redux.
• Sync Firebase authentication with Redux while preserving account-specific drafts in local storage.
• Prevent pending build requests from updating state after switching accounts.
• Centralize notifications with optional navigation buttons and support for displaying them inside modals.
• Add authentication tests and update existing component and saved-build tests.

Related issues

Closes #110

Verification

Run from frontend/:

• npm test — all 106 tests passed across 11 test files.
• npm run lint — passed.
• npm run build — passed, with a bundle-size warning for the main JavaScript chunk.

Manual browser testing was also performed to ensure that functionality stayed the same.

Screenshots

Not included applicable.

Checklist

• I have reviewed my own changes.
• The changes meet the linked issue's acceptance criteria, where applicable.
• I have verified the changes and recorded the results above.
• I have added or updated tests where needed.
• I have included screenshots for visual changes, or marked them not applicable.