F9: Responsive/mobile pass — usable on phones and tablets #49

Part of Phase 1.1 (epic #14). Spec requires it: wireframes include a Mobile Daily Entry design; tech spec KD-6 targets a PWA used in barns. Phase 1.0 shipped desktop-tuned CSS with zero media queries. Offline capture (KD-4) is deliberately NOT this issue — filed separately for later.

Problems today

• Topbar: 8 nav links, no wrap/collapse — horizontal overflow on phones.
• Tables (table.data, min-width 24rem) sit directly in the page — force whole-page horizontal scroll.
• Touch targets (button.link, row actions) below comfortable tap size.
• No @media breakpoints anywhere.

Scope

• Collapse nav on narrow screens (hamburger or wrap — simplest thing that works).
• Wrap all data tables in overflow-x: auto containers; page body never scrolls horizontally.
• Touch-friendly sizing for buttons/inputs at phone widths (44px-ish targets).
• Daily entry flow verified at ~390px against the mobile wireframe (specs/product/wireframes/mobile_daily_entry.svg) — this is the primary barn-phone screen.
• Dashboard/Stock/Flocks/Grades/Customers/Sales/History spot-checked at phone + tablet widths.
• Keep desktop layout unchanged.

Acceptance

• Every screen usable at 390px (phone) and 768px (tablet) with no horizontal page scroll.
• Daily entry: record + submit comfortably one-handed on a phone viewport.
• Verified with real browser drives at mobile viewport sizes (screenshots on the PR).