Condenser: UI shim layer mapping @decky/ui to condenser.ui

[mdeguzis]

Bind our existing src/ui/ components (Button, Dropdown, Fields, Modal, SidebarNavigation, Spinner, Focusable, showModal) to the condenser.ui surface instead of @decky/ui.

condenser.ui already gives us Focusable, SidebarNavigation, Tabs, Menu, MenuItem, showModal, showContextMenu, showToast, and cls button/input classes. The higher-level fields are not provided, so build ToggleField, SliderField, DropdownItem, PanelSection, ConfirmModal, ModalRoot, DialogButton, TextField from cls + Focusable.

Our actual @decky/ui surface is small: Focusable, DialogButton, showModal, ModalRoot, Navigation, then a few Dropdown/Toggle/Text/Confirm uses.

[mdeguzis]

UI shim is in. src/ui/condenser/index.tsx exposes the @decky/ui surface backed by condenser.ui (Focusable, Menu, MenuItem, showContextMenu) plus our standalone src/ui components, with real implementations for the parts condenser does not ship: ConfirmModal (with a working closer, the gap noted on #100), PanelSection, PanelSectionRow, ButtonItem, DialogCheckbox. Navigation/Router map to condenser.nav. src/ui/condenser/api.ts maps callable/toaster/fetchNoCors through platform().

build.mjs aliases @decky/ui and @decky/api at esbuild, so existing tabs and modals compile unchanged. Verified the built frontend has zero @decky imports and routes through the shims. Remaining: Patch (needs condenser.tree fiber patching) and openFilePicker are stubbed, and the real tabs still need to be pulled in once the backend port (#101) provides their actions.