refactor(app): remove non-idempotent side effects and async loads from QueryaApp.build() #1345

Problem

In lib/app/app.dart, the root widget QueryaApp.build executes several non-idempotent side effects:

@override
Widget build(BuildContext context) {
  installAppWiring();
  QueryaCommandRegistry.instance.ensureCoreDefaults();
  unawaited(LocalExtensionRegistry.instance.load());
  ...

1. In Flutter, Widget.build() must be pure and idempotent. Executing setup logic, registering global commands, and initiating background async I/O scans on every widget rebuild violates this contract.
2. In lib/main.dart (line 23), installAppWiring() is already invoked during startup prior to runApp().
3. Any rebuild of the root widget (e.g. hot reload, platform brightness changes, or scale updates) triggers LocalExtensionRegistry.instance.load() and command re-registration again.

Code Location

• lib/app/app.dart (lines 22–26)

UI Kit Relationship

• App Root Layer (Not UI Kit): Lives in lib/app/app.dart.
• Related Open Issue: Connects with architectural cleanup refactor(arch): eliminate reverse imports from lib/core into lib/features #1239 (refactor(arch): eliminate reverse imports from lib/core into lib/features), which introduced lib/app/app_wiring.dart to resolve reverse imports.

Proposed Solution

1. Remove installAppWiring(), ensureCoreDefaults(), and LocalExtensionRegistry.instance.load() from QueryaApp.build().
2. Move one-time startup initialization to main() in lib/main.dart, or convert QueryaApp to a StatefulWidget and run these tasks once in initState().

Acceptance Criteria

• QueryaApp.build() contains zero side effects or asynchronous I/O dispatches.
• Hot reload and root widget rebuilds do not trigger duplicate extension scans or wiring routines.