Refresh logo and diagrams

[danbarr]

Updates the logos and README file for the Stacklok rebrand.

Large PR Justification

• Changed lines are mostly SVG files.

[github-actions]

Large PR Detected

This PR exceeds 1000 lines of changes and requires justification before it can be reviewed.

How to unblock this PR:

Add a section to your PR description with the following format:

## Large PR Justification

[Explain why this PR must be large, such as:]
- Generated code that cannot be split
- Large refactoring that must be atomic
- Multiple related changes that would break if separated
- Migration or data transformation

Alternative:

Consider splitting this PR into smaller, focused changes (< 1000 lines each) for easier review and reduced risk.

See our Contributing Guidelines for more details.

---

This review will be automatically dismissed once you add the justification section.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 57.15%. Comparing base (5fd5ef6) to head (ee9d46b).
⚠️ Report is 6 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3206      +/-   ##
==========================================
+ Coverage   57.10%   57.15%   +0.05%     
==========================================
  Files         346      346              
  Lines       34304    34314      +10     
==========================================
+ Hits        19588    19612      +24     
+ Misses      13096    13075      -21     
- Partials     1620     1627       +7     

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Large PR justification has been provided. Thank you!

[github-actions]

✅ Large PR justification has been provided. The size review has been dismissed and this PR can now proceed with normal review.