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/ui/sale_sheet.dart

@@ -132,14 +132,31 @@ class _SaleSheetState extends State<_SaleSheet> {
                     controller: _currency,
                     decoration: InputDecoration(
                       labelText: t.sale.currency,
-                      helperText: t.sale.currencyHint,
-                      helperMaxLines: 2,
                       border: const OutlineInputBorder(),
                     ),
+                    onChanged: (_) => setState(() {}),
                   ),
                 ),
               ],
             ),
+            const SizedBox(height: 8),
+            // Quick picks so a currency is one tap. Ğ1 sits quietly among the
+            // familiar ones — offered, never imposed — and free text still takes
+            // anything else.
+            Wrap(
+              spacing: 8,
+              children: [
+                for (final c in ['€', 'Ğ1', t.sale.hours])
+                  ChoiceChip(
+                    key: Key('sale.currencyChip.$c'),
+                    label: Text(c),
+                    selected: _currency.text.trim() == c,
+                    onSelected: (sel) => setState(() {
+                      _currency.text = sel ? c : '';
+                    }),
+                  ),
+              ],
+            ),
             const SizedBox(height: 12),
             TextField(
               key: const Key('sale.note'),