#9237: Fix: WhatsApp QR code not rendering in chat

Fixes #9231 ## Problem When running the WhatsApp login tool via `/pair whatsapp` command or the `whatsapp_login` agent tool, the QR code was not displaying in the chat interface. Users saw a blank gray box instead of the QR code image. ## Root Cause The markdown sanitizer in `ui/src/ui/markdown.ts` was configured to strip out `<img>` tags during HTML sanitization. The `allowedTags` array didn't include `"img"`, causing DOMPurify to remove all image tags from the rendered markdown. When the WhatsApp login tool returns the QR code as markdown: ```markdown  ``` The markdown renderer converted it to an `<img>` tag, but then DOMPurify stripped it out during sanitization, leaving no visible content. ## Solution Added `"img"` to the `allowedTags` array and `"src"` + `"alt"` to the `allowedAttrs` array in the markdown sanitizer configuration. This allows: - Images rendered from markdown to display properly - Both `src` and `alt` attributes to be preserved for accessibility - Data URLs (base64 encoded images) to work correctly ## Changes - `ui/src/ui/markdown.ts`: - Added `"img"` to `allowedTags` (line 23) - Added `"alt"` and `"src"` to `allowedAttrs` (line 38, alphabetically sorted) ## Impact ✅ WhatsApp QR codes now render correctly in chat ✅ Other markdown images (if used elsewhere) will now work ✅ No breaking changes - only enables previously blocked feature ✅ Minimal security impact - DOMPurify still sanitizes other dangerous content ## Testing - ✅ TypeScript compilation passes - ✅ Code formatted with oxfmt - ✅ Only 2 lines changed in 1 file Manual testing needed: Run WhatsApp login tool and verify QR code displays in chat. <!-- greptile_comment --> <h2>Greptile Overview</h2> <h3>Greptile Summary</h3> This PR updates the UI markdown sanitizer (`ui/src/ui/markdown.ts`) to allow `<img>` tags and the `src`/`alt` attributes so markdown-rendered images (including the WhatsApp pairing QR code emitted as ``) are no longer stripped by DOMPurify and can display in chat/tool output renders. The main behavioral change is that any sanitized markdown rendered via `toSanitizedMarkdownHtml()` can now include images. <h3>Confidence Score: 3/5</h3> - This PR is likely safe but expands markdown rendering surface area in a way that needs tighter constraints. - Change is small and targeted, but allowing `<img src>` in sanitized user/assistant markdown can introduce a concrete privacy leak via remote image loads unless `src` is constrained (e.g., to `data:image/*`). - ui/src/ui/markdown.ts <!-- greptile_other_comments_section --> **Context used:** - Context from `dashboard` - CLAUDE.md ([source](https://app.greptile.com/review/custom-context?memory=fd949e91-5c3a-4ab5-90a1-cbe184fd6ce8)) - Context from `dashboard` - AGENTS.md ([source](https://app.greptile.com/review/custom-context?memory=0d0c8278-ef8e-4d6c-ab21-f5527e322f13)) <!-- /greptile_comment -->