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/ast.i18n.json

@@ -94,6 +94,7 @@
     "langEs": "Español",
     "langEn": "English",
     "langPt": "Português",
+    "langPtBr": "Português (Brasil)",
     "langAst": "Asturianu",
     "langFr": "Français",
     "langDe": "Deutsch",
@@ -146,9 +147,9 @@
     "license": "Llicencia",
     "licenseValue": "AGPL-3.0",
     "website": "Sitiu web",
-  "sourceCode": "Códigu fonte",
-  "translate": "Ayuda a traducir",
-  "translateSubtitle": "Ayuda a traer Tane a la to llingua",
+    "sourceCode": "Códigu fonte",
+    "translate": "Ayuda a traducir",
+    "translateSubtitle": "Ayuda a traer Tane a la to llingua",
     "openSourceLicenses": "Llicencies de códigu abiertu",
     "openSourceLicensesSubtitle": "Biblioteques de terceros y les sos llicencies",
     "copyright": "© {years} Asociación Comunes, baxo AGPLv3"