chore: add full app dev shortcut

[naufaldi]

What Change

• Added pnpm dev:app as a friendly shortcut for tauri dev.
• Updated README development docs to recommend pnpm dev:app for full local app testing.
• Removed the quick-start suggestion to run the whole dev app with sudo; helper installation should stay behind the explicit privileged-helper flow.

Why Change

• Local testing needed a single obvious command for the full app path.
• tauri dev already runs dev:prepare-helper through beforeDevCommand, so the alias gives a clearer command without duplicating helper/build logic.
• Avoiding sudo pnpm tauri dev keeps normal development safer and closer to the intended helper architecture.

Impact

• Affected areas: package scripts and README development instructions.
• Breaking changes: No.
• Dependencies: No new dependencies.
• Testing: Verified package.json resolves dev:app to tauri dev; verified pnpm exec tauri --version; verified pnpm run dev:prepare-helper builds fanguard-helper successfully.