[Sync Framework] Migrate budget-tracker to sync framework (add sync for first time)

[Michael-Obele]

Overview

Migrate budget-tracker to the centralized sync framework. This app currently has no server sync (only sharing features implemented) — this migration adds sync for the first time using the framework.

Design doc: docs/plans/2026-06-21-sync-framework-design.md

Current state

• src/routes/apps/(app)/budget-tracker/+page.svelte — PersistedState only, no server sync, AUTO_BACKUP_DELAY = 3000 defined but unused
• src/lib/budget-tracker/states.svelte.ts — PersistedState for budgets, selectedExpenses, budgetStrikethrough
• src/lib/remote/budget-tracker.remote.ts — only sharing functions (getBudgetShareSettings, setBudgetSharing, regenerateBudgetShareLink) — no backup/load functions

Migration steps

• Create app DB with createReactiveDB:

  const db = createReactiveDB({
    name: 'budget-tracker',
    version: 1,
    stores: {
      budgets: { keyPath: 'id' },
      expenses: { keyPath: 'id' },
    },
  });

• Replace PersistedState with db.budgets.liveAll(), db.expenses.liveAll()
• Keep selectedExpenses and budgetStrikethrough as local-only state (UI state, not synced)
• Add sync to budget-tracker.remote.ts:
  • createLoadQuery for loadBudgetData (new — loads budgets + expenses)
  • createBackupForm for backupBudgetForm (new)
  • createBackupCommand for backupBudgetCommand (new)
  • Keep existing sharing functions
• Create SyncManager with auto-backup trigger:

  strategy: timestampMerge,
  trigger: 'auto-backup',
  autoBackupDelay: 3000,  // keep existing intended delay

• Update +page.svelte — add sync.syncOnMount(data), backup button, sync button
• Add +page.server.ts — load budget data for authenticated users (new file)
• Run bun check + svelte-autofixer
• Test sync (first time this app has cloud sync!)

What stays app-specific

• Sharing features (getBudgetShareSettings, setBudgetSharing, regenerateBudgetShareLink)
• UI state (selectedExpenses, budgetStrikethrough) — local-only, not synced
• Data types (Budget, Expense)

Prisma models (existing)

• Budget → store budgets
• Expense → store expenses (nested in budget)

Blocked by

• [Sync Framework] Build centralized sync framework in src/lib/sync/ #23 — Framework PR
• [Sync Framework] Migrate medication-tracker to sync framework (pilot) #24 — Medication-tracker pilot