Task 046 - Prompt Input Tailwind Refactor

Goal

Port the prompt input stack to Tailwind utilities and shared tokens so it no longer depends on custom selectors in src/index.css.

Tasks 043-045 complete (color and typography tokens available, message item refactored).

src/components/prompt-input.tsx and nested elements use Tailwind + token classes for layout, borders, and typography.
Legacy selectors in src/index.css matching .prompt-input-container, .prompt-input-wrapper, .prompt-input, .send-button, .prompt-input-hints, .hint, .hint kbd, and related variants are removed or replaced with token-based utilities.
Input states (focus, disabled, multi-line expansion) and keyboard hint row look identical in light/dark modes.
Esc debounce handling and attachment hooks remain functional.

Audit existing markup in prompt-input.tsx and note the current class usage.
Replace className strings with Tailwind utility stacks that reference CSS variables (e.g., bg-[var(--surface-base)], text-[var(--text-muted)]).
Introduce small reusable helpers (e.g., .kbd token utility) in src/styles/components.css if patterns recur elsewhere.
Delete superseded CSS blocks from src/index.css once equivalents exist.
Verify light/dark theme parity and interaction states manually.

Run npm run build.
In dev mode, send a message with/without attachments, toggle disabled state, and confirm keyboard hints render correctly.

0.75 hours