[jay23606]

Fixes #717

Add the existing MathCAT logo to the user, translator, and developer guides, matching the library-users page.

Validation

• Before: the issue was confirmed in the source—the logo was absent from these three pages. The Rust and docs test commands were not run on the base branch.
• After: the Jekyll site build passes and the generated pages include the logo; cargo test and cargo test --features no-unsafe pass; cargo clippy and cargo clippy --features no-unsafe pass with warnings denied; git diff --check passes.
• Not verified: visual appearance in a browser.

🤖 Generated with Claude Code

[moritz-gross]

issue #717 says:

Note: this is not #406.: the logo exists but it is either not present or not really designed properly for these pages.

How is this handled?