## Why
### Problem
The dashboard page takes ~4 seconds to load for users with many balance
records. Profiling revealed 29 queries across the initial page load + 3
separate API calls, a 576 KB wasted payload from unused bank records,
and a critical 3.7s bottleneck in `BalanceLookup` correlated subqueries.
## What
### Changes
**Query optimizations:**
- Replace correlated `MAX()` subqueries in `BalanceLookup` with
derived-table `joinSub` pattern — **48x faster** (3,693ms → 77ms) on
accounts with thousands of balance records
- Replace `whereHas` (EXISTS subqueries) with JOINs in
`DashboardAnalyticsController` and `CashflowAnalyticsController` — ~3x
faster per query
- Cache encryption check results in `HandleInertiaRequests` middleware
to avoid 2 duplicate queries per request
**Payload & request reduction:**
- Remove dead `banks` query from `DashboardController` (2,365 records,
576 KB never used by frontend)
- Remove duplicate `categories` and `accounts` queries already provided
by middleware shared props
- Consolidate 3 separate `fetch()` API calls into Inertia v2
`Inertia::defer()` props grouped under `'dashboard'` (single follow-up
request with skeleton fallbacks)
**Frontend:**
- Replace `useDashboardData` fetch hook with `usePage()` props +
`<Deferred>` components
- Convert `CashflowSummaryCard` from internal fetch to prop-based
- Use `router.reload({ only: [...] })` for balance update refetch
### Performance summary
| Metric | Before | After |
|--------|--------|-------|
| Initial page queries | 16 | 12 |
| Follow-up HTTP requests | 3 separate API calls | 1 Inertia deferred |
| BalanceLookup time | 3,693ms | 77ms |
| Wasted payload | 576 KB | 0 |
## Verification
### Tests
All 633 feature tests pass, including 40 dashboard/cashflow-specific
tests.
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