feat(desktop): render tool output images as attachments (#13643)

* fix(desktop): render tool output images as attachments

Add support for displaying media returned by tool calls (e.g. screenshots)
as rendered images with expand-to-fullscreen capability instead of raw
base64 text. Introduces an `ImageCarousel` component for navigating
multiple images, propagates the expand handler to tool message blocks,
and extracts/validates output media in tool summaries.

* test: cover multi-image and canonical media extraction in tool output (#13645)

extractOutputMedia and the desktop tool-message rendering path were only
ever exercised with exactly one distinct valid image, and
canonicalInlineMedia (MCP-style type: "media" blocks for audio/video/file)
had zero coverage. Add tests for: multiple distinct images in one tool
result (parser + desktop carousel navigation), inline audio via the
mime_type key spelling, canonical video/file media blocks, and rejection
of an invalid canonical image block.

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Co-authored-by: Harrison <harrison@cline.bot>