Three chat-panel fixes that share `ai_chat_panel.rs` / `input.rs` /
`scroll.rs`, so they land together:
- Model picker scoped to connected agents: discovery still probes
every installed CLI into `chat.discovered_models`, but the picker
lists only providers the user connected (`rebuild_available_models`,
re-run on connect-toggle + discovery). Connect state persists in
settings.json. The dropdown is height-capped, scrolls (wheel /
trackpad) with a thumb, and tints the hovered row.
- Chat input wraps: long input flows across up to 3 visible rows,
clipped + bottom-anchored, instead of overflowing the panel edge.
- perf: a canvas pan / zoom no longer marks the layout scene dirty
— it only moves the viewport transform, so re-running the taffy
layout solve + skia text measurement every drag frame was pure
waste. The repaint still re-applies the viewport.
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