Rewrite App to local-first contact debt tracker with 3-party cycle detection and import/export

[unclehowell]

Motivation

• Replace the previous complex, multi-component DCC ledger with a simpler, local-first contact-based debt tracker focused on GBP balances and offline portability.
• Provide an easy export/import workflow and surface 3-party debt cancellation opportunities for small group reconciliation.

Description

• Reimplemented App.tsx to a self-contained React + TypeScript UI that stores per-contact debts (name, email, theyOweMeGbp, iOweThemGbp) in localStorage under the key dcc-circle-cache-v1 and removed the previous multi-component architecture and many unused imports.
• Added cleanMoney normalization, ContactDebt and Edge types, and hooks for loading/saving cached rows, plus an exportedBase64 representation for easy sharing.
• Implemented edge construction and 3-party cycle detection (me -> A -> B -> me) with cancellable amount calculation and de-duplication of suggestions.
• Added UI for adding/removing rows, viewing people & debts, copying/exporting the Base64 string, and importing a Base64 dataset with validation and ID repair, and updated README.md to document features and local development steps.

Testing

• No automated tests were run against these changes.

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Codex Task

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