fix: green brand theme, iOS launcher icon, password reveal, real login error

- Theme primary now the iOS brand green (#20A050), fixed app-wide (was tied
  to the server's blue primary_color)
- Launcher icon generated from the iOS AppIcon across all densities;
  dropped the placeholder adaptive icon
- PasswordField: eye toggle + brief last-character reveal; used on login,
  profile and CalDAV password inputs
- Login now surfaces the server's actual error detail (verified the JSON
  contract against the live server; a 401 is a genuine credential mismatch)
- CLAUDE.md: correct prod base URL to calendar.scarriffle.com

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

app/src/main/res/mipmap-anydpi-v26/ic_launcher.xml

@@ -1,4 +0,0 @@
-<adaptive-icon xmlns:android="http://schemas.android.com/apk/res/android">
-    <background android:drawable="@color/ic_launcher_background" />
-    <foreground android:drawable="@drawable/ic_launcher_foreground" />
-</adaptive-icon>

app/src/main/res/mipmap-anydpi-v26/ic_launcher_round.xml

@@ -1,4 +0,0 @@
-<adaptive-icon xmlns:android="http://schemas.android.com/apk/res/android">
-    <background android:drawable="@color/ic_launcher_background" />
-    <foreground android:drawable="@drawable/ic_launcher_foreground" />
-</adaptive-icon>