Feedback form branding: color customization + logo upload/hosting

Problem: The guest-facing feedback form's branding currently only supports a logo referenced by an external hosted URL. If that URL breaks or changes, the logo silently fails to load. There's also no color customization for the form.

Request: Improve feedback-form branding: (a) allow direct logo upload with Sparrow hosting the image (removing dependence on a customer-supplied external URL), and (b) add color customization so the form can match brand palette.

Detail:

• Today: logo must be a hosted URL entered in brand settings; no upload option; no color controls.
• Desired: upload-and-host logo; configurable brand colors on the guest feedback form.
• Motivation: external URLs are fragile; customers often have logo files but not hosted URLs.

Acceptance criteria:

• User can upload a logo file and Sparrow hosts/serves it on the feedback form.
• User can set brand color(s) applied to the feedback form.
• Existing hosted-URL logos continue to work (backward compatible).