Add launch-time notification permission prompt and UI polish

- Request POST_NOTIFICATIONS once on first app launch, with a
  plain-language rationale dialog shown before the OS prompt
  (permission_handler), since upload/download progress relies on it.
- ShareUploadView no longer shows "More tabs" - there's nowhere useful
  for it to go mid-upload.
- FloatingBottomNavBar's pill scrolls horizontally instead of
  overflowing when the visible tab set doesn't fit.
- Settings account card: drop the separate server-address row and its
  globe icon, showing the host inline with the quota percentage/
  "Unlimited storage" text instead (left-aligned, same size).

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

pubspec.lock

@@ -712,6 +712,54 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "2.11.0"
+  permission_handler:
+    dependency: "direct main"
+    description:
+      name: permission_handler
+      sha256: "59adad729136f01ea9e35a48f5d1395e25cba6cea552249ddbe9cf950f5d7849"
+      url: "https://pub.dev"
+    source: hosted
+    version: "11.4.0"
+  permission_handler_android:
+    dependency: transitive
+    description:
+      name: permission_handler_android
+      sha256: d3971dcdd76182a0c198c096b5db2f0884b0d4196723d21a866fc4cdea057ebc
+      url: "https://pub.dev"
+    source: hosted
+    version: "12.1.0"
+  permission_handler_apple:
+    dependency: transitive
+    description:
+      name: permission_handler_apple
+      sha256: f49cb15a064ea9d974fc7fbb302099353b7b170d07284e86e264561579e5bcf8
+      url: "https://pub.dev"
+    source: hosted
+    version: "9.6.1"
+  permission_handler_html:
+    dependency: transitive
+    description:
+      name: permission_handler_html
+      sha256: "6ea98b3f17f60d3b527f2647ed2ab4dc0f6bfe25b22cb1c363f5d8f62252f6ac"
+      url: "https://pub.dev"
+    source: hosted
+    version: "0.1.4+1"
+  permission_handler_platform_interface:
+    dependency: transitive
+    description:
+      name: permission_handler_platform_interface
+      sha256: ed86a61c190258fdd65de395ea0632822e3415c1faec38eae0c31b479c28a531
+      url: "https://pub.dev"
+    source: hosted
+    version: "4.4.1"
+  permission_handler_windows:
+    dependency: transitive
+    description:
+      name: permission_handler_windows
+      sha256: caeae01858a0a7d2df67a445ac98e1ad95e55a0e77c73044f4e9b1c8c2289cbd
+      url: "https://pub.dev"
+    source: hosted
+    version: "0.2.2"
   petitparser:
     dependency: transitive
     description: