drive-by: update links for pro banners

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---

> [!NOTE]
> Revamps ChatErrorBox with styled CTA buttons, UTM-tracked links,
broader error matching, and adds default help CTAs; updates Pro banners
to point to /pro URLs.
> 
> - **Chat**:
> - **Error handling/UI**: Expands rate-limit matching to include
`"Provider returned error"` and appends default CTAs on generic errors.
> - **CTAs**: Replaces underlined links with styled buttons via
`ExternalLink` (supports `primary|secondary` variants and icons), and
adds upgrade/docs buttons across error states.
> - **Links**: Adds UTM parameters to Pro/Docs links; updates exceeded
budget CTA to `"Reload or upgrade your subscription"` with new
subscription URL.
> - **Pro Banners**:
> - Adjusts banner click-through URLs in `AiAccessBanner`,
`SmartContextBanner`, and `TurboBanner` to `https://www.dyad.sh/pro?...`
(removes `#ai`).
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
2111954ac9a98dd66f5b3b9e628270ac19713a2d. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
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