Refresh stale Local Offline Store tech chapter #690

The mobile tech chapter still calls the phone's offline store a JSON-backed candidate with SQLite as the alternative, but the phone's outbox has been a SQLite store since the offline-outbox work. A new session would re-rate and rewrite that chapter.

Context

In the Backlog repository (JSdotNet/Backlog), .devbook/tech/mobile.md chapter ## Local Offline Store says status: candidate, "JSON-backed on-device storage", with alternatives: ["SQLite"]. That is stale: since PR #652 (capture-outbox) the phone keeps its outbox, cached inbox and task view in SQLite ΓÇö see src/App/Backlog.Mobile.UI/Outbox/SqliteDeviceStore.cs, src/App/Backlog.Mobile.UI/Tasks/SqliteTaskViewStore.cs, and the Microsoft.Data.Sqlite reference in src/App/Backlog.Mobile.UI/Backlog.Mobile.UI.csproj. .devbook/arc42/06-runtime-view.md#mobile-capture-and-sync already describes a SQLite outbox. Update the tech chapter to rate the store as adopted SQLite (Microsoft.Data.Sqlite), fix its depends-on/alternatives/prose, and follow .agents/rules/devbook-tech.md and .agents/rules/devbook-chapter-metadata.md. This is a devbook-folder change: route it through the repository's flow-spec flow. Run node tools/devbook/check-metadata.mjs (0 blocking) before committing.

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