Data Refactor Phase 1: Add accountId to transactions with automatic migration

[Copilot]

Summary

This PR implements Phase 1 of the data refactor by adding an accountId field to all transaction objects and providing automatic migration for existing data. This prepares the codebase for a future unified transaction store by ensuring every transaction knows which account it belongs to.

Changes

Transaction Schema & Data Model

• Added required accountId field to the transaction schema validation
• Updated generateTransaction() to accept and include accountId in all new transactions
• Enhanced transaction actions (createNewTransaction, createRepeatTransaction) to pass accountId when creating transactions
• Added ACCOUNT_ID constant to TransactionFields enum

Redux State Management

• Modified account reducers to ensure accountId is set when transactions are added or updated
• Transactions are now guaranteed to have accountId when stored in account arrays

Automatic Migration

Implemented an idempotent migration in store.js that:

• Automatically detects transactions missing accountId on app load
• Backfills accountId from the parent account for existing transactions
• Reports migration progress to the console with per-account and total counts
• Immediately persists migrated data to localStorage
• Only runs when needed - skips transactions that already have accountId

Example migration output:

Migration: Added accountId to 2 transactions in account "Test Checking"
Migration: Added accountId to 1 transactions in account "Test Savings"  
Migration: Successfully updated 3 transactions across 2 accounts

Testing

Migration Testing

• Simulated old data without accountId - migration successfully backfilled the field
• Reloaded application multiple times - migration correctly identified already-migrated data (idempotent)
• Verified migrated data persists correctly to localStorage

New Transaction Testing

• Created new transactions through UI - verified accountId is automatically included
• Tested repeated transaction creation - all generated transactions include accountId

Build & Lint

• ✅ All linting passes
• ✅ Production build completes successfully
• ✅ No runtime errors

Acceptance Criteria

All acceptance criteria from the issue have been met:

• ✅ Each transaction object includes a valid accountId
• ✅ Existing transactions are updated with their respective accountId
• ✅ New transactions persist with accountId automatically
• ✅ Migration is idempotent and safe to re-run
• ✅ Migration reports the number of transactions updated per account

Screenshots

Application running with version 1.9.0-rc.1 showing migrated data:

Impact

This change is backwards compatible and non-breaking:

• Existing users' data is automatically migrated on first load
• The migration is transparent and requires no user action
• All application functionality continues to work as before
• Prepares the foundation for Phase 2: creating a unified transaction store

Related Issues

Closes #[issue-number]
Depends on #50 (Data Refactor Phase 0: Rename Redux slices to legacy)

Original prompt

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This section details on the original issue you should resolve

<issue_title>Data Refactor Phase 1: Add accountId to transactions</issue_title>
<issue_description>Summary

Prepare for a unified transaction store by adding an accountId field to all transaction objects and backfilling existing data.

Goals
• Add accountId to the transaction type.
• Backfill existing persisted data so every transaction includes the correct accountId.
• Ensure new transactions are saved with accountId.
• Implement a one-time migration that updates all existing data in place.

Acceptance Criteria
• Each transaction object includes a valid accountId.
• Existing transactions are updated with their respective accountId.
• New transactions persist with accountId automatically.
• Migration is idempotent and safe to re-run.
• Migration reports the number of transactions updated per account.</issue_description>

Comments on the Issue (you are @copilot in this section)

@jwaspin #50 Is a prerequisite

Fixes #46

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