UI Quick Fixes

Three targeted CSS/HTML fixes resolving a spurious navigation warning, toast overlap with the nav header, and misaligned columns across grouped fetch schedule tables.

What Was Built

• Import wizard submit form now disables the confirm-navigation Stimulus controller on submit, preventing a spurious beforeunload/turbo:before-visit dialog after the import completes
• Toast notification container repositioned from top-4 to top-16 so toasts render below the 64px nav header
• Dashboard fetch schedule tables use table-fixed layout with explicit percentage column widths (45/15/22/18%) so each time-bracket group's columns align consistently

Files Modified

• app/views/source_monitor/import_sessions/steps/_confirm.html.erb -- added data: { action: "submit->confirm-navigation#disable" } to the confirm-step form_with
• app/views/layouts/source_monitor/application.html.erb -- changed top-4 to top-16 on toast container div
• app/views/source_monitor/dashboard/_fetch_schedule.html.erb -- added table-fixed class to table; added explicit w-[45%], w-[15%], w-[22%], w-[18%] widths to column headers