add pro banners (#1269)

<!-- This is an auto-generated description by cubic. -->

## Summary by cubic
Adds rotating Pro banners on the home page to promote Dyad Pro (AI
access, Smart Context savings, Turbo speed). Also tightens the home
layout and centers the setup headline.

- New Features
- Added ProBanner with three variants (AI Access, Smart Context, Turbo).
One shows at random and links to dyad.sh/pro with UTM tags.
- Banners are hidden when Pro is enabled or the user has a budget
(settings.enableDyadPro or userBudget).
- Added OpenAI, Google, and Anthropic logo assets for the AI Access
banner.
- Home updates: show 3 inspiration prompts (was 5), center and constrain
layout, and render ProBanner below content.
  - SetupBanner heading is centered and slightly smaller (text-5xl).

<!-- End of auto-generated description by cubic. -->

assets/ai-logos/google-logo.svg

@@ -0,0 +1 @@
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