Closes #585.

Currently, there are at least two places where an Electron logo appears
instead of the Dyad logo:
- In the Windows control panel (see #585).
- On the taskbar (or equivalent) of some Linux desktop environments
while running the app.

The Windows installer (`.Setup.exe`) also shows a generic icon instead
of the Dyad logo when viewed in the file explorer.

This PR aims to fix all of the above. It's a relatively minor detail,
but it's nice to have anyway.

The relevant documentation from Electron Forge is on this page:

https://www.electronforge.io/guides/create-and-add-icons#setting-the-app-icon

I've double-checked that this fixes the icons on Windows 10, XFCE and
Cinnamon (on Linux Mint), and GNOME (on Fedora). I don't have a device
that runs Windows 11.
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<!-- This is an auto-generated description by cubic. -->
---
## Summary by cubic
Replace generic/Electron icons with the Dyad logo across Windows and
Linux. Ensures correct branding in the Windows control panel, Linux
taskbar, and the Windows installer.

- **Bug Fixes**
  - Set BrowserWindow icon to assets/icon/logo.png.
  - Configured Electron Forge makers:
- Squirrel: iconUrl and setupIcon set to Dyad .ico for installer and
control panel.
    - Deb/RPM: icon set to Dyad .png for desktop environments.
- Verified on Windows 10, Linux Mint (XFCE, Cinnamon), and Fedora
(GNOME).

<sup>Written for commit 2f29dcc2fd34fdc53fb9bd2126cf02a7bd719920.
Summary will update on new commits.</sup>

<!-- End of auto-generated description by cubic. -->

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Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>