[pratikbuilds]

Add PromptInputToolbar with an add menu, icon buttons, model and mode pickers, a float above the box, a context chip and a note. The pickers are select-only comboboxes and the add menu is a menu button; both keep or return focus to their trigger and need no optional peer. A toolbar placed last in PromptInput takes its own row.

Stacked on #5: review only this commit. Part of corbitsdev#94.

Notes for review

• Toolbar parts take their own disabled; PromptInput's context stays private, so a host disabling the prompt passes disabled to the toolbar parts too.
• No reasoning-level choice in the model picker; onValueChange stays a single id.
• One class added to PromptInput's root so a trailing toolbar wraps onto its own row (e2e checks with and without a toolbar).
• Escape in pickers/menu stops bubble-phase listeners (as the suggestions list does); untested inside a dialog.

Verification

• This commit passes bun run typecheck and bun run lint on its own (the stack is checked commit by commit).
• At the top of the stack: bun run check, bun run build, bun run dep-guard, bun run contrast-test and bun run test:e2e (Playwright specs and the Storybook axe sweep in light and dark) pass.

Closes corbitsdev#103

[pratikbuilds]

Moved upstream: corbitsdev#118