fix: make settings dialog scrollable

[60dage]

Summary

• constrain the Settings dialog to the available popover height
• enable vertical scrolling when its content exceeds that height
• reuse the same max-h-[88vh] / overflow-y-auto pattern already used by ServiceForm

The Agent Radar hook rows can make Settings taller than the webview. Since the dialog is vertically centered and the root clips overflow, its top and bottom could become inaccessible.

Closes #3

Testing

• npm test — 8 passed
• npx tsc --noEmit
• npm run build
• cargo test --manifest-path src-tauri/Cargo.toml — 95 passed
• cargo build --manifest-path src-tauri/Cargo.toml