Rework model selector with loadout-backed slots

[senxd]

Summary

• Rebuild the model picker on top of the five-slot loadout: slots carry harness, model, effort, provider model options, and a per-slot activation shortcut
• Per-slot shortcut recording with physical-key conflict detection against the keymap, other loadouts, and reserved composer/app chords; Some("") disables a slot shortcut while None keeps the positional mod-shift-N default
• Slot cards reorder via drag-and-drop or arrow keys, keeping model options and shortcuts attached to the card; provider catalog columns reorder the same way and persist a device-local provider_order
• Slot menus split into frosted root + submenu cards (agent / model / effort / model options / speed / shortcut / remove) with full keyboard navigation, replacing the single glass slab over union bounds
• Catalog requests are scoped to the effective device and workspace cwd, and reload on scope change; pending agent selections never persist an empty model
• Claude harness passes model[1m] idempotently via a shared model_argument helper; picker rows show each row's resolved loadout shortcut badge
• Split the loadout page into loadout/{bindings,cards,catalog,indicator,options}.rs and add extensive unit + gpui tests (shortcut normalization, reorder semantics, menu navigation, macOS shifted-digit aliases)

Screenshots

Redesigned the model selector (Reasoning bar, repositioned layout)	Custom model loadouts

Test plan

• cargo check --workspace --all-targets
• cargo test -p zeron-ui loadout (67 tests)
• cargo fmt --check
• Manual: record/clear/reorder slot shortcuts on macOS and verify Cmd+Shift+1-5 defaults still work
• Manual: drag models from provider columns (incl. OpenRouter partition) into slots

Generated with Devin

[senxd]

Also this was not listed above but the Pi provider in the model selector respects the model filter that is set in the Pi config. It should accurately represent what /models looks like in the pi cli.