fix: stray "0" shown for steps with no timer (v0.52.1)

`{step.timerSeconds && (...)}` renders the literal 0 when timerSeconds is
the number 0 rather than null/undefined — only false/null/undefined skip
rendering in JSX, a bare falsy number doesn't. Some steps ended up with
timerSeconds stored as 0 instead of null (e.g. AI generation filling in a
"default" value for an optional field rather than omitting it), which
this guard then rendered as a bare "0" instead of hiding the timer.

Fixed at all 4 render sites (recipe page, cook mode, both print views) by
coercing to a real boolean (`!!step.timerSeconds`) — makes a stored 0
behave identically to null everywhere it's displayed.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

apps/web/app/print/[id]/page.tsx

@@ -171,7 +171,7 @@ export default async function RecipePrintPage({ params }: Params) {
                 {recipe.steps.map((step) => (
                   <li key={step.id}>
                     {step.instruction}
-                    {step.timerSeconds && (
+                    {!!step.timerSeconds && (
                       <span className="timer">⏱ {Math.floor(step.timerSeconds / 60)} min</span>
                     )}
                   </li>