[TASK] TASK-02: Refactor custom_shell.html Initialization Hooks

[ikostan]

TASK-02: Refactor custom_shell.html Initialization Hooks

Description

Reconfigure the engine bootstrap sequence inside custom_shell.html to integrate download tracking metrics inside the template object scope instead of appending parameter overrides to the runtime startGame() lifecycle execution promise.

Technical Steps

1. Locate the engine instance initialization script section at the base of custom_shell.html.
2. Declare a consolidated customConfig object that references the structural elements of $GODOT_CONFIG.
3. Inject a dedicated onProgress(current, total) method callback within this configuration mapping layout to output tracking logs ("Telemetry - Assembly Transfer: X%") onto the browser console.
4. Bind this explicit tracking configuration definition directly to the initialization execution signature: var engine = new Engine(customConfig);.

Acceptance Criteria

• The console properly streams progressive assembly transfer data when running cold boots or simulating data throttling profiles.
• The runtime engine context binds to the WebGL target canvas frame layers cleanly.
• The DOM layout successfully drops #loading layers and applies defensive aria-hidden tags once the application layer initialization finishes.