Command search inputs and MCP form fields have no accessible name

Problem

Screen readers announce several search and form fields without a name.

Command pickers (search lists). cmdk 1.1.1 always renders a hidden <label for> that holds the label prop of Command and points the input at it. None of the six pickers passes label: chat/ModelEffortPicker.tsx:505, chat/ModelSelector.tsx:215, panels/BranchPicker.tsx:140, panels/FontPicker.tsx:140, panels/NewWorkspaceDialog.tsx:884, shell/layout/workbenchTabs.tsx:353. The empty label also takes priority over the placeholder, so Chromium computes the combobox name as "". The shared wrapper packages/ui/command.tsx:7-17 doesn't require the prop.
MCP server dialogs. Field (panels/McpServerDialogs.tsx:133-157) renders its label as a plain <span> that isn't linked to its control. As a result:
- text inputs are named only by their placeholder;
- the raw-entry Textarea at :933 has no name at all;
- the transport, exposure, tier and scope toggle sets (:316, :380, :732, :741) are read as bare toggle buttons without the field name.

Make label required on @thinkrail/ui/command (on Command or CommandInput) and pass a locale key at each call site.
Link MCP Field labels to their controls (<label htmlFor> or aria-labelledby with useId). Name the toggle sets as a group, or switch them to SegmentedControl (see the duplicate-primitives issue).
Add unit checks with getByRole("combobox", { name }) so a missing name fails a test.

Found while documenting the component library in #1075.