Scaffold the Flutter app with Italian l10n and region configuration

Creates the app skeleton and the seam everything else in the project hangs
off: region-specific data lives in an asset file, not in code, so adding a
region later is a new JSON file rather than a refactor.

Notable choices:

- applicationId and namespace are it.nuvolari.app rather than the doubled
  it.nuvolari.nuvolari that `flutter create` produces, with the Kotlin package
  and the iOS bundle identifiers moved to match.
- SDK levels are pinned instead of inherited from `flutter.*`. Google Play
  requires API 36, and that is a release blocker rather than something to let a
  Flutter upgrade change silently. minSdk 24 is the highest floor the planned
  dependencies impose.
- Riverpod and Dio-free for now, no code generation: see docs/stack-decisions.md.
- Italian is the l10n source language, so app_it.arb is the template rather
  than a translation of an English original.

The region parser rejects rather than repairs. An inverted bounding box, a map
centre outside its own bounds, an unknown adapter name, a duplicate zone code
or an empty attribution list all throw with the offending field named. Each of
those would otherwise fail silently and visibly wrong: a swapped latitude and
longitude renders the radar in the wrong place, an unknown adapter falling back
to mock would show demo frames where live data was expected, and a missing
attribution is a licence violation rather than a cosmetic gap.

Tests run against the asset that actually ships and against a captured copy of
the live ARPA CAP feed, so the eleven zone codes in the config are checked
against the eleven the feed really emits rather than against a list retyped
from documentation.

Verified: dart format clean, flutter analyze 0 issues, 50 tests passing,
flutter build appbundle --debug produces an AAB with applicationId
it.nuvolari.app, minSdk 24, targetSdk 36.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Nuvolari/app/assets/regions/piemonte.json

@@ -0,0 +1,71 @@
+{
+  "id": "piemonte",
+  "displayName": "Piemonte",
+  "timeZone": "Europe/Rome",
+
+  "bbox": [6.55, 43.95, 9.30, 46.55],
+
+  "map": {
+    "center": [7.95, 45.25],
+    "zoom": { "min": 6.0, "max": 13.0, "initial": 7.2 }
+  },
+
+  "sources": {
+    "radar": {
+      "defaultAdapter": "mock",
+      "availableAdapters": ["mock", "dpc"],
+      "product": "VMI",
+      "frameIntervalMinutes": 5
+    },
+    "forecast": {
+      "defaultAdapter": "metno",
+      "availableAdapters": ["metno"]
+    },
+    "alerts": {
+      "defaultAdapter": "arpaCap",
+      "availableAdapters": ["arpaCap"],
+      "officialBulletinUrl": "https://www.arpa.piemonte.it/rischi_naturali/boll/bollettino_allerta.pdf"
+    }
+  },
+
+  "alertZones": [
+    { "code": "Piem-A", "name": "Toce", "provinces": ["NO", "VB"] },
+    { "code": "Piem-B", "name": "Val Sesia, Cervo e Chiusella", "provinces": ["BI", "NO", "TO", "VC"] },
+    { "code": "Piem-C", "name": "Valli Orco, Lanzo, bassa Val Susa e Sangone", "provinces": ["TO"] },
+    { "code": "Piem-D", "name": "Alta Val Susa, Valli Chisone, Pellice e Po", "provinces": ["CN", "TO"] },
+    { "code": "Piem-E", "name": "Valli Varaita, Maira e Stura", "provinces": ["CN"] },
+    { "code": "Piem-F", "name": "Valle Tanaro", "provinces": ["CN"] },
+    { "code": "Piem-G", "name": "Belbo e Bormida", "provinces": ["AL", "AT", "CN"] },
+    { "code": "Piem-H", "name": "Scrivia", "provinces": ["AL"] },
+    { "code": "Piem-I", "name": "Pianura Settentrionale", "provinces": ["AL", "AT", "BI", "NO", "TO", "VC"] },
+    { "code": "Piem-L", "name": "Pianura Torinese e Colline", "provinces": ["AL", "AT", "CN", "TO"] },
+    { "code": "Piem-M", "name": "Pianura Cuneese", "provinces": ["CN", "TO"] }
+  ],
+
+  "attributions": [
+    {
+      "id": "dpc",
+      "text": "Radar-DPC — Dipartimento della Protezione Civile",
+      "license": "CC BY-SA",
+      "url": "https://radar.protezionecivile.it"
+    },
+    {
+      "id": "metno",
+      "text": "MET Norway",
+      "license": "CC BY 4.0",
+      "url": "https://api.met.no"
+    },
+    {
+      "id": "arpa",
+      "text": "Arpa Piemonte",
+      "license": null,
+      "url": "https://www.arpa.piemonte.it"
+    },
+    {
+      "id": "osm",
+      "text": "© OpenStreetMap contributors",
+      "license": "ODbL",
+      "url": "https://www.openstreetmap.org/copyright"
+    }
+  ]
+}