RayRAG v0.7.9 — a button for the navigation generator

RayRAG v0.7.9

An API with no button is a feature the user cannot reach

v0.7.8 made POST /datasets/{id}/navigation work. Nothing in the UI called it — the same shape as
three earlier findings this phase (the Overview label, the knowledge-graph entry, and now this). So the
button was added in the very next release.

The dataset Overview panel now has Build navigation tree. It calls the endpoint and reports
what actually happened rather than a bare "done":

• Generated N of M document(s);
• plus skipped K without parsed chunks when documents had no parsed chunks;
• the error text in red on failure, and data.message when present (for example "this dataset has no
  chunks").

Verified in the browser, not just by curl

Deployed build 0.7.9: the button exists, clicking it shows GENERATED 1 OF 1 DOCUMENT(S). and the
page reports 0 errors — so the navigation tree really is built from the UI, matching the API result
measured in the previous round.

2145 tests pass, 0 failures (123 KB-UI tests included).