Architecture: golden contract for task rows and run views #25

From the architecture review of 2026-10-23 (on fe9ba27; #1-#3 of that review are done and on main 2c19448). Re-check line numbers before building.

The JSON the UI reads (task rows, run views) has no contract test. Example drift: a report task's result: "report" falls outside the TS union.

Idea: golden JSON files written by Java tests and type-checked by the UI build. Speculative.