refactor(frontend): consolidate Home card options into a single state object

[marcalexiei]

HomeScreen held ~16 separate useState hooks for card options and threaded them through 34 props into CustomizeStage.
This consolidates them into a single typed CardOptions state object (new pages/Home/cardOptions.ts), updated via a keyed setter.

Changes

• CustomizeStage props go from 34 to 5; buildCardUrl takes userId, selectedCard and options.
• Stage descriptions move into STAGE_LABELS, replacing a positional string array in the JSX.
• The three GitHub-URL paste handlers in CustomizeStage share one pastedPathTail helper.
• A failed OAuth authenticate call left the page stuck on the loading spinner;
  the exchange now runs in try/catch/finally and the redirect is parsed with
  URLSearchParams instead of substring matching.

[vercel]

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