Guard Mermaid rendering against dagre panics

[zachlloyd]

Description

• Bump mermaid_to_svg to a commit that makes dagre_rust::intersect_rect handle degenerate center-point intersections without panicking.
• Add a Warp-side guard around Mermaid SVG rendering so future renderer panics become failed Mermaid assets instead of crashing the client.
• Add unit coverage for the Warp-side panic-to-error path.

Upstream dependency PR: warpdotdev/mermaid-to-svg#16

No new log statements were added.

Linked Issue

N/A - Slack crash-cluster investigation from #dev-crash-clusters.

Testing

• cargo fmt --manifest-path /workspace/warp/Cargo.toml --all --check

• CARGO_BUILD_JOBS=1 cargo nextest run --manifest-path /workspace/warp/Cargo.toml --no-fail-fast --workspace mermaid_renderer_panic_returns_error

• CARGO_BUILD_JOBS=1 cargo check --manifest-path /workspace/warp/Cargo.toml -p warp_editor

• CARGO_BUILD_JOBS=1 cargo clippy --manifest-path /workspace/warp/Cargo.toml -p warp_editor --no-deps

• I have manually tested my changes locally with ./script/run

Screenshots / Videos

N/A - crash containment/dependency fix with automated coverage.

Agent Mode

• Warp Agent Mode - This PR was created via Warp's AI Agent Mode

CHANGELOG-BUG-FIX: Fixed a Mermaid rendering crash caused by degenerate Dagre edge intersections.

Conversation: https://staging.warp.dev/conversation/2381ce85-50ab-49ff-a15b-1f8d84dc3196
Run: https://oz.staging.warp.dev/runs/019e8a8d-7abf-793f-9859-6dbd1ac7de30
This PR was generated with Oz.