"Build Corpora" jumbo popdown — the strategy/thesis curator gets a real front door

A header-level dropdown (the Lossless 'jumbo popdown' convention, ported from astro-knots into the shell's Svelte header) replaces the memorized-:3017-port habit with a click: 'Flows' -> 'Build Corpora' navigates straight to strategy-curator, full-screen, no CSV-augmentation steps trailing it. No new persisted state, no auth interaction — a plain navigate action, same mechanism the chat rail and pack-runner already use to reach non-rotation remotes.