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_en.g.dart

@@ -1638,6 +1638,9 @@ class Translations$sale$en {
 	/// en: '€, Ğ1, hours… (optional)'
 	String get currencyHint => '€, Ğ1, hours… (optional)';
 
+	/// en: 'hours'
+	String get hours => 'hours';
+
 	/// en: 'Note (optional)'
 	String get note => 'Note (optional)';
 
@@ -2563,6 +2566,7 @@ extension on Translations {
 			'sale.amount' => 'Amount',
 			'sale.currency' => 'Currency',
 			'sale.currencyHint' => '€, Ğ1, hours… (optional)',
+			'sale.hours' => 'hours',
 			'sale.note' => 'Note (optional)',
 			'sale.save' => 'Save',
 			'sale.delete' => 'Remove',