webui-rs 3/6: Datastar shell + server-rendered pages (runs list, run overview, program detail)

[GeorgePearse]

Depends on #26, #27.

Rebuild the current React pages as server-rendered HTML fragments patched by Datastar. No client framework, no JS charting libs.

Pages

1. Runs list — table of experiments, click → run overview
2. Run overview — generation table, current best, island summary, novelty-gate verdicts; chart placeholders filled by webui-rs 4/6: Live updates over SSE — kill the 3s client polling loop #29
3. Program detail — code view, metrics, parent + inspirations links

Mechanics

• Navigation via Datastar (data-on-click → server patches the main region), URL kept honest with history so deep links work — the current React app uses react-router, don't regress shareable URLs
• Filters/sort on the programs table as Datastar signals round-tripped to the server (server does the filtering, mirrors how the current backend takes query params)
• Code view: server-side syntax highlighting (e.g. syntect) — no highlight.js
• Templating: pick one of maud/askama/hypertext and stick with it (maud pairs nicely with fragment-heavy Datastar apps)

Definition of done

Feature parity with the read-only views of the React app, measured against the pages listed in docs/webui.md.