nx_ui_exec_gate.nx

nx_ui_exec_gate.nx -- EXECUTION verification (task #35, operator 2026-07-04: "the Nishi team should SEE everything ... i shouldnt have to find bugs"). The static eyes prove a button is WIRED; this proves a button WORKS: the sovereign JS engine now models DOM events (addEventListener + element.click()), so a gate can WIRE a handler, FIRE it like a user tap, and assert the DOM actually CHANGED. This is the rung that turns "wired" into "works" -- the difference that let the dead-buttons bug ship past serving+static checks. Drives js_render_page (parse -> tree -> run scripts -> serialize) on the engine's real path. NEG-CONTROLS prove the mutation is CAUSED by the fired click, not spurious. 0=GREEN / 1=RED.