Responsive/mobile: make the app usable on small screens

[ApocDev]

The app is effectively desktop-only right now — most views (block editor, sidebar, factory, summary matrix, browse, assistant) don't lay out or work usefully on phones or small/narrow screens.

Status: far-future / not urgent

Tracking this so it isn't lost. No work planned soon — the product is desktop-first for now. Revisit once the planner feature set has settled.

Scope (when we get to it)

• Audit each route for small-screen breakage (block.$id editor, the blocks sidebar, factory, the production/summary matrix, browse, whatif/coherence, assistant).
• Sidebar → collapsible drawer on narrow widths.
• Wide data tables (summary matrix, block rows) need a responsive/scroll strategy rather than overflow.
• Touch interactions for the drag/drop surfaces (sidebar folders, future recipe-row reorder Block view: drag/drop to reorder recipe rows #6/Sidebar: nested folders (folders inside folders) #8).
• Establish breakpoints/conventions in the Tailwind v4 setup so new UI is responsive by default.