feat(inventory): additive CSV import for bulk digitization

Import a spreadsheet list (the same 21-column schema the CSV export
already produces) as new varieties/lots. Tolerant reader: columns
matched by header name in any order, only variety_label required,
unknown enums fall back to a safe default, rows sharing variety_id
collapse into one variety with several lots. Species re-linked by
scientific name. Additive by design (fresh ids + HLC), so it never
overwrites existing rows; JSON stays the canonical id-reconciling import.

Adds a hand-rolled RFC 4180 parser (no new dependency), an importCsv
path in VarietyRepository/ExportImportService, an 'Import from CSV'
tile in the backup section, and en/es strings.

Note: i18n .g.dart also carries pre-existing About/intro strings from
the working tree (regenerated by slang).

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

@@ -51,12 +51,17 @@
     "exportJsonSubtitle": "Complete copy, can be imported back",
     "importJson": "Import from JSON",
     "importJsonSubtitle": "Merge a saved copy into this inventory",
+    "importCsv": "Import from CSV",
+    "importCsvSubtitle": "Add a list from a spreadsheet",
     "importConfirmTitle": "Import a saved copy?",
     "importConfirmBody": "Entries merge with your inventory; when the same entry exists on both sides, the newest version wins. Nothing gets duplicated.",
+    "importCsvConfirmTitle": "Import a CSV list?",
+    "importCsvConfirmBody": "Every row is added as a new entry. This does not merge or replace, so importing the same file twice adds it twice.",
     "importAction": "Import",
     "exportSaved": "Copy saved",
     "cancelled": "Cancelled",
     "importDone": "Imported: {added} new, {updated} updated",
+    "importCsvDone": "Imported {count} from CSV",
     "importFailed": "This file could not be read as a Tanemaki copy",
     "failed": "Something went wrong"
   },
@@ -73,6 +78,34 @@
     "openSourceLicenses": "Open-source licenses",
     "openSourceLicensesSubtitle": "Third-party libraries and their licenses"
   },
+  "intro": {
+    "skip": "Skip",
+    "next": "Next",
+    "start": "Get started",
+    "menuEntry": "How Tanemaki works",
+    "slides": {
+      "welcome": {
+        "title": "The seed that brought you here",
+        "body": "Every traditional seed is a letter written by thousands of generations, passed from hand to hand. We are what we are thanks to that sharing."
+      },
+      "inventory": {
+        "title": "Your seed bank, in your pocket",
+        "body": "Note what you have, from which year, how much and where it came from — with the name you use. A photo and a name are enough to start."
+      },
+      "privacy": {
+        "title": "Yours, and only yours",
+        "body": "No account, no internet, no trackers. Your data lives encrypted on your device, and only what you choose is ever shared."
+      },
+      "share": {
+        "title": "Share, the way it's always been done",
+        "body": "Offer what you have spare — gift, swap or sell — and let someone nearby find it. Only an approximate distance is shown, never your address; you close the deal in person."
+      },
+      "plantare": {
+        "title": "To sow is to multiply",
+        "body": "With a Plantare, whoever receives seed promises to return some later. And since returning it means growing it, every loan multiplies the commons."
+      }
+    }
+  },
   "inventory": {
     "title": "Inventory",
     "searchHint": "Search seeds",