Fix stale docs claiming web persistence is in-memory only

Web actually persists via localStorage (LocalStorageStores.kt), which
survives page reloads — only SQLDelight itself isn't used there, since
its web driver needs a worker plus a wasm sqlite binary. The doc
comments and AGENTS.md still described the in-memory state this
replaced.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FXcrACM5sok3M1KQJ8kByy

AGENTS.md

@@ -12,12 +12,9 @@ and Android (see README's Supported Platforms/Download and Install). Web and
 Desktop/JVM are real future release targets too — `desktopApp` already has
 full native packaging configured (DMG/MSI/DEB, see its `build.gradle.kts`) —
 but neither has a release/CI pipeline set up yet, so treat them as
-not-yet-shipped rather than dev-only. Web specifically also has no real
-persistence yet (see `data/db/SqlDelightStores.kt`'s doc comment: no
-SQLDelight driver, in-memory only, nothing survives a page reload) — worth
-keeping in mind if that platform's release plans firm up. The app converts
-between BTC, Sats, and fiat currencies using live exchange rates (Coinbase,
-CoinGecko, or a manually typed-in rate).
+not-yet-shipped rather than dev-only. The app converts between BTC, Sats,
+and fiat currencies using live exchange rates (Coinbase, CoinGecko, or a
+manually typed-in rate).
 
 This is a from-scratch rewrite of an earlier Skip-based (Swift-transpiled-to-
 Kotlin) implementation — `main` is now this Kotlin Multiplatform project.
@@ -146,9 +143,11 @@ to call.
 SQLDelight (`data/db/SqlDelightStores.kt` + platform-specific driver
 `actual`s) backs `ExchangeRateStore`/`SelectedCurrenciesStore`/
 `SelectedSourceStore`, each exposed via an `expect fun createXStore()`
-factory. Web has no real SQLDelight driver — it gets an in-memory-only
-fallback (nothing persists across a page reload). This is a known gap to
-close if/when Web's release plans firm up, not a permanent design choice.
+factory. Web has no real SQLDelight driver — SQLDelight's web driver needs a
+worker plus a wasm sqlite binary — so it gets a `localStorage`-backed
+fallback instead (`data/db/LocalStorageStores.kt`), which does survive page
+reloads, just scoped to the browser profile/origin (cleared by clearing
+site data, not shared across browsers/devices).
 
 ## Testing and verification