feat(ux): usable amounts, colour-coded category/form chips, currency quick-picks

Four usability passes across the everyday flows:

- Quantity picker: a countable unit (cob/pod/ear…) now defaults to 1 and
  the stepper clamps at a minimum of 1 — you can never store 'a cob' with
  a blank/zero figure. Vibe units (a few) still carry no number.
- Category & form chips are colour-coded (new category_palette.dart): a
  small muted earthy palette maps each botanical family to a STABLE
  tonality (fill + readable ink), and each lot form gets its own tone.
  Applied to the inventory filter bar (now grouped attributes | forms |
  families, separated by a hairline), the list's category headers (a
  matching colour dot), and the lot-form selector.
- Sale currency: quick-pick chips (€ · Ğ1 · hours) fill the field in one
  tap — Ğ1 offered quietly among familiar options, never imposed — while
  free text still takes anything else. New i18n key sale.hours (en/es/pt/ast).

Tests: quantity_picker_test (default-1, clamp, vibe, clear-still-1),
category_palette_test (stable/distinct swatches); overflow guard + the
inventory widget tests stay green.

apps/app_seeds/lib/i18n/strings.g.dart

@@ -4,9 +4,9 @@
 /// To regenerate, run: `dart run slang`
 ///
 /// Locales: 4
-/// Strings: 1828 (457 per locale)
+/// Strings: 1832 (458 per locale)
 ///
-/// Built on 2026-07-11 at 00:20 UTC
+/// Built on 2026-07-11 at 04:03 UTC
 
 // coverage:ignore-file
 // ignore_for_file: type=lint, unused_import