feat(02-02): create room providers, form screen, icon picker, and router routes

- Add Riverpod providers (roomWithStatsList, RoomActions) connecting to RoomsDao
- Create RoomFormScreen with name field, icon picker preview, create/edit modes
- Create IconPickerSheet bottom sheet with curated Material Icons grid
- Add nested GoRouter routes: /rooms/new, /rooms/:roomId, /rooms/:roomId/edit
- Add placeholder TaskListScreen and TaskFormScreen for Plan 03 routes
- Add 11 new German localization keys for room management UI
- Add flutter_reorderable_grid_view dependency

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

lib/l10n/app_de.arb

@@ -23,5 +23,21 @@
     "placeholders": {
       "version": { "type": "String" }
     }
-  }
+  },
+  "roomFormCreateTitle": "Raum erstellen",
+  "roomFormEditTitle": "Raum bearbeiten",
+  "roomFormNameLabel": "Raumname",
+  "roomFormNameHint": "z.B. K\u00fcche, Badezimmer...",
+  "roomFormNameRequired": "Bitte einen Namen eingeben",
+  "roomFormIconLabel": "Symbol w\u00e4hlen",
+  "roomDeleteConfirmTitle": "Raum l\u00f6schen?",
+  "roomDeleteConfirmMessage": "Der Raum und alle zugeh\u00f6rigen Aufgaben werden unwiderruflich gel\u00f6scht.",
+  "roomDeleteConfirmAction": "L\u00f6schen",
+  "roomCardDueCount": "{count} f\u00e4llig",
+  "@roomCardDueCount": {
+    "placeholders": {
+      "count": { "type": "int" }
+    }
+  },
+  "cancel": "Abbrechen"
 }