feat(i18n): complete Portuguese, add Brazilian Portuguese (pt_BR)

Fill the ~74 UI strings pt.i18n.json was missing (saved searches, label
scanning, Plantaré, lot history), then add pt_BR as a proper Brazilian
variant rather than a copy of European Portuguese: tu/teu/tua -> você/
seu/sua with matching verb conjugation, partilhar -> compartilhar, and
Guardar -> Salvar for UI actions (seed-saving keeps "guardar", the
correct term in both variants). Wires AppLocale.ptBr into the language
picker and regenerates slang output.

apps/app_seeds/lib/i18n/fr.i18n.json

@@ -95,6 +95,7 @@
     "langEs": "Español",
     "langEn": "English",
     "langPt": "Português",
+    "langPtBr": "Português (Brasil)",
     "langAst": "Asturianu",
     "langFr": "Français",
     "langDe": "Deutsch",
@@ -147,9 +148,9 @@
     "license": "Licence",
     "licenseValue": "AGPL-3.0",
     "website": "Site web",
-  "sourceCode": "Code source",
-  "translate": "Aider à traduire",
-  "translateSubtitle": "Aidez à traduire Tane dans votre langue",
+    "sourceCode": "Code source",
+    "translate": "Aider à traduire",
+    "translateSubtitle": "Aidez à traduire Tane dans votre langue",
     "openSourceLicenses": "Licences open source",
     "openSourceLicensesSubtitle": "Bibliothèques tiers et leurs licences",
     "copyright": "© {years} Association Comunes, sous AGPLv3"