chore(js-ts): Convert Base/Keypad to TypeScript

[devin-ai-integration]

Summary

Part of Workstream 2 (Base & UI component JS→TS migration). Converts the entire app/components/Base/Keypad/ component folder (5 source files) from JS to TS. Type-only change — snapshot and all 282 unit tests are identical/passing.

• createKeypadRule.js → .ts
• constants.js → .ts
• useCurrency.js → .ts
• components.js → .tsx
• index.js → .tsx

The two test files (Keypad.test.js, createKeypadRule.test.js) are intentionally left as .js: Keypad.test.js uses enzyme whose types aren't installed, and per the migration rules we don't add new @types packages. They import the renamed .ts/.tsx source unchanged.

Worth knowing (rest is mechanical PropTypes→interface):

• createKeypadRule now returns a typed KeypadHandler = (currentAmount: string, inputKey: string) => string. Its options are { decimalSeparator?: string | null; decimals?: number | false | null }. The decimals === false branch is kept — createKeypadRule.test.js exercises decimals: false (separator suppressed), so false is a real runtime value, not dead code.
• hasDecimals(decimalSeparator, decimals) is called as hasDecimals(String(decimalSeparator), String(decimals)). hasDecimals already string-interpolates both args, so this reproduces the previous coercion exactly (e.g. null → "null"), keeping the generated regex byte-identical.
• CURRENCIES typed as Record<string, Currency> where Currency = { decimalSeparator: string | null; handler: KeypadHandler; symbol: string | null }; KEYS is as const.
• components.tsx: compound Keypad statics attached via Object.assign(KeypadContainer, { Row, Button, DeleteButton }) (behavior-identical to the previous Keypad.Row = ... mutations). Sub-components typed from ViewProps/TouchableOpacityProps with textStyle?: StyleProp<TextStyle>.
• index.tsx: onChange?: (data: KeypadChangeData) => void (PropTypes had it optional) called via onChange?.(...); value ?? '' passed to the handler (handler maps both '' and undefined to '0', so identical).

Validation (local)

• yarn lint:tsc: passes, 0 errors.
• eslint on all 5 files: clean (no any).
• yarn jest app/components/Base/Keypad: 282 tests pass, 1 snapshot identical.

CI note

The install-gated CI jobs on this fork fail before reaching any TS/test step due to a preexisting broken dependency (react-native-tcp pins a GitHub commit that now 404s on yarn install); check-diff/CLABot/label checks also fail on all fork PRs for preexisting infra/governance reasons (ruby/setup-ruby detects the macOS runner as self-hosted). None are caused by this diff, which contains only file renames + type annotations and no lockfile change.

Link to Devin session: https://app.devin.ai/sessions/a0f7f796d1fb45e88b2feabe5829a4ac
Requested by: @WesternConcrete

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