fix(security): DOMPurify updated due dependabot warnings

[WebReflection]

Update DOMPurify from 3.4.2 (and 3.3.1 in session-ui) to 3.4.13 to resolve open Dependabot alerts.

What changed

• Root package.json: catalog + overrides dompurify → 3.4.13
• packages/ui/package.json and packages/session-ui/package.json: direct dependency → 3.4.13
• bun.lock: single resolved dompurify@3.4.13 across the workspace

Why

3.4.2/3.3.1 are affected by several advisories (prototype pollution and XSS bypasses), including:

• GHSA-v9jr-rg53-9pgp / CVE-2026-41238
• GHSA-cj63-jhhr-wcxv / CVE-2026-65913
• CVE-2026-49459, CVE-2026-65900, CVE-2026-65901, CVE-2026-65902
• GHSA-748c-f84h-hp2v / CVE-2026-75838 (fixed in 3.4.13)

Updating the root override is the key fix: it currently forces every consumer — including the transitive dompurify used by mermaid and posthog-js — back to the vulnerable 3.4.2.

Validation

• bun install resolves dompurify@3.4.13 workspace-wide
• packages/ui and packages/session-ui typecheck clean
• All tests pass: ui 160 pass, session-ui 81 pass
• Sanitization behavior verified identical between 3.4.2 and 3.4.13 under jsdom: script/style stripping, onclick removal, SVG/foreignObject preservation (incl. the Mermaid HTML_INTEGRATION_POINTS config)

Supersedes dependabot PRs #12439 and #13012, which only bumped the direct deps without fixing the root override.

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Files Reviewed (5 files)

• .changeset/dompurify-security-update.md
• bun.lock
• package.json
• packages/session-ui/package.json
• packages/ui/package.json

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