feat: add DocumentSegment for inline HTML/SVG/Mermaid rendering #115

Job	Run time
Package compatibility / Node 22	30s
Prepare verification matrix	9s
Package compatibility / Node 24	26s
Verify / architecture	15s
Verify / lint-changed	15s
Verify / test	24s
Verify / audit	11s
Verify / lint	11s
Verify / typecheck	31s
Verify / build-webui	9s
Gate	4s
	3m 5s

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