Fix failing tests: savings tab rename + frequency utility

[Copilot]

Three CI tests were failing on issue-fixes due to an unupdated test after an intentional tab rename and a behavioral regression introduced during a refactor of bill frequency logic.

Summary

• tabManagement.ts: Renamed benefits tab → savings (order: 3), shifted loans to order 4. Added normalizeLegacyTabId() for backward-compat migration of persisted configs. Refactored initializeTabConfigs to sync canonical labels/icons from defaults while preserving user visibility/order state.
• frequency.ts (new): Centralized frequency normalization and occurrences-per-year lookups for pay, bill, and savings frequencies. Handles aliases (biweekly, semiannual, annually, etc.) and input normalization (case, spacing, dash variants).
• billFrequency.ts: Refactored to use getBillFrequencyOccurrencesPerYear. custom frequency explicitly returns amount * 12 — preserving original monthly semantics independent of the generic frequency utility's fallback of 1.
• payPeriod.ts: getPaychecksPerYear now delegates to getPayFrequencyOccurrencesPerYear.
• auth.ts: Added CoreFrequency, SavingsFrequency types; PayFrequency and BillFrequency now derived from CoreFrequency.
• tabManagement.test.ts: Updated expected tab order to reflect savings/loans positions.
• frequency.test.ts (new): 4 tests covering normalization, pay/bill/savings frequency lookups including aliases.

Result: 46 tests passing across 12 test files.

Type of Change

• Bug fix
• New feature
• Refactor/cleanup
• Documentation update
• Build/release/config update

User-Facing Impact

• This PR changes user-facing behavior
• If user-facing behavior changed, I updated Features.md

Docs Checklist

• I reviewed README.md and updated it for major functionality/architecture changes (if applicable)
• I updated app_updates/APP_UPDATES.md for shipped/planned status changes (if applicable)

Validation

• npm run lint
• npx tsc --noEmit
• Manual smoke test completed

Notes

• normalizeLegacyTabId maps old benefits IDs → savings so existing persisted tab configs migrate cleanly on load.
• getBillFrequencyOccurrencesPerYear('custom') intentionally returns 1 (no period given = unknown cadence); convertBillToYearly short-circuits before calling it so bill calculation semantics are unchanged.

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[github-actions]

❌ Version File Not Updated

The version file was not modified in this PR. Please update the version file in the root directory with the new version number.