Function mountEditor

Mounts the hex editor screen into container for the given loadedFile.

Mounting order:

1. Inject the HTML template and read the file buffer.
2. Initialise core/editor with the buffer.
3. Cache DOM element references.
4. Set header metadata (filename, format badge).
5. Wire up close / open buttons.
6. Build structured and signature offset sets for hex-view colouring.
7. Mount toolbar, hex-view, inspector, status-bar, and sidebar.
8. Subscribe to selection and editor-change events.
9. Attach hover listeners for cursor tracking.
10. Synchronise the initial column layout.