webui-rs 6/6: Server-rendered SVG lineage tree + cutover (delete webui/frontend and backend_server.py)

[GeorgePearse]

Depends on #28, #29, #30. Final issue — ends with the old stack deleted.

Lineage tree

• Layout computed server-side from the /api/experiments/{run_id}/lineage read model (webui-rs 2/6: Port the read model — ClickHouse queries + typed rows in Rust, parity-tested against the FastAPI responses #27). Lineage is mostly single-chain with island migrations — a layered/Sugiyama-lite layout in plain Rust should be enough; fall back to graphviz via layout-rs only if hand layout gets ugly
• Emit SVG with one <g id="program-{id}"> per node; data-on-click → server patches the program-detail panel (webui-rs 3/6: Datastar shell + server-rendered pages (runs list, run overview, program detail) #28). Hover highlight via CSS
• Pan/zoom if needed: CSS transform on the SVG viewport driven by a couple of Datastar signals — still no JS libs
• Live: new nodes appear via SSE fragment patches (webui-rs 4/6: Live updates over SSE — kill the 3s client polling loop #29)

Cutover checklist

• Parity pass against docs/webui.md features; note anything intentionally dropped
• genesis webui CLI launches the Rust binary (decide distribution: cargo build --release in dev docs vs shipping a prebuilt binary; the Python package must not silently depend on a Rust toolchain at runtime without saying so)
• Update docs/webui.md + README screenshots
• Delete genesis/webui/frontend/ (React 19, Vite, d3, chart.js, plotly, react-router, playwright config) and genesis/webui/backend_server.py
• Drop the golden-file parity harness from webui-rs 2/6: Port the read model — ClickHouse queries + typed rows in Rust, parity-tested against the FastAPI responses #27 once green