Fix current UI and AI panel issues

[IAmJSD]

Summary

• simplify the update prompt and condense the photo-search model copy
• prevent the AI panel from reading or generating Codex memories
• keep large size labels on one line
• add a themed custom title bar on macOS
• render the text caret with contrast on light and dark content

Verification

• make app PROFILE=debug
• cargo test --workspace
• cargo clippy -p schist-app -p schist-tools-type --all-targets -- -D warnings
• git diff --check main...HEAD

Fixes #108.
Fixes #109.
Fixes #110.
Fixes #111.
Fixes #112.
Fixes #113.