feat(block1): variety detail + edit screen with reactive lots

Tapping an inventory item now opens its detail (the /variety/:id route was a
placeholder). Read + edit one variety end-to-end:

- Detail view: photo, category, "also known as" names, notes and lots, driven
  by a reactive VarietyDetailCubit.
- Edit core fields (label/category/notes, LWW) via a bottom sheet.
- Add a lot (harvest year + quantity) — the list refreshes reactively.
- Soft-delete (tombstone) with a confirm dialog.

Repository:
- watchVariety(id): merges Drift table-change streams (variety, lots, names,
  attachments) via StreamGroup and reloads the full detail on any change, so a
  lot added to a *different* table still refreshes the view.
- updateVariety (LWW), addLot, softDeleteVariety.

i18n: detail/edit/addLot strings (ES/EN); switched slang to {param} braces
interpolation (translator- and Weblate-friendly).

Tests: repository (reactive watchVariety, update, soft-delete) and widget tests
(render, edit updates title, add-lot appears, delete shows not-found). Full
suite green: 23 passing, 1 skipped (SQLCipher-only encryption guard).

apps/app_seeds/lib/i18n/en.i18n.json

@@ -2,6 +2,12 @@
   "app": {
     "title": "Tanemaki"
   },
+  "common": {
+    "save": "Save",
+    "cancel": "Cancel",
+    "delete": "Delete",
+    "edit": "Edit"
+  },
   "inventory": {
     "title": "Inventory",
     "searchHint": "Search seeds",
@@ -18,6 +24,28 @@
     "save": "Save",
     "cancel": "Cancel"
   },
+  "detail": {
+    "notFound": "This seed is no longer here.",
+    "lots": "Lots",
+    "noLots": "No lots yet.",
+    "names": "Also known as",
+    "notes": "Notes",
+    "addLot": "Add lot",
+    "deleteConfirm": "Delete this seed?",
+    "year": "Year {year}",
+    "noYear": "Year unknown"
+  },
+  "editVariety": {
+    "title": "Edit seed",
+    "name": "Name",
+    "category": "Category",
+    "notes": "Notes"
+  },
+  "addLot": {
+    "title": "Add lot",
+    "year": "Harvest year",
+    "quantity": "Quantity"
+  },
   "quantityKind": {
     "aFew": "a few",
     "some": "some",