Add model management and macOS integration

AGENTS.md

@@ -4,6 +4,13 @@
 - Keep changes focused, handle errors explicitly, and add the smallest useful test for non-trivial behavior.
 - Preserve `rustfmt` output and keep Clippy warning-free.
 
+## Visual language
+
+- Follow the Codex macOS dark UI: near-black backgrounds, subtly raised surfaces, quiet borders, rounded corners, and restrained contrast.
+- Present overviews as one bordered panel with divided rows, a clear primary label, muted supporting text, and compact trailing actions.
+- Reuse the shared surface and action-button styles in `src/app/view.rs`; keep button shape, padding, typography, hover, and disabled states consistent across windows. Destructive actions may differ by color only, while navigation controls may remain flat.
+- Prefer generous spacing and clear hierarchy over decoration; avoid one-off colors, card stacks, oversized controls, and screen-specific button styling.
+
 ## Commit gates
 
 Run before every commit: