Change the logo and emblem to the new approved Varbase brand logo

Problem/Motivation

The project still ships the old Varbase emblem (the blue square with arrows).
Varbase now has a new approved brand logo: the varbase wordmark
with the blue smile emblem, defined in the approved VB stylesheet and logo
design files.

Proposed resolution

Replace the old logo and emblem assets with the new approved ones:

• logo.png, new 512×512 square smile emblem.
• Full wordmark logo SVG/PNG (where the project ships one).
• Emblem color / white / grey variants (where shipped).
• favicon.ico, new emblem favicon (where shipped).
• Navigation sidebar emblem (where the project sets it).

Remaining tasks

• ✅ File an issue about this project
• ✅ Addition/Change/Update/Fix to this project
• ✅ Testing to ensure no regression
• ➖ Automated unit/functional testing coverage
• ➖ Developer Documentation support on feature change/addition
• ➖ User Guide Documentation support on feature change/addition
• ➖ UX/UI designer responsibilities
• ➖ Accessibility and Readability
• ✅ Code review from 1 Varbase core team member
• ✅ Full testing and approval
• ✅ Credit contributors
• ✅ Review with the product owner
• ✅ Update Release Notes
• ✅ Release varbase-11.0.0-alpha3, varbase_starter-1.0.0-alpha2, varbase_ai_safety-1.0.0-alpha3

User interface changes

• N/A

API changes

• N/A

Data model changes

• N/A

Release notes snippet

• chore: #3603604 New approved Varbase brand logo, wordmark, and favicon for Varbase AI Safety