avatar: Show placeholder on image load error.

Previously, if an avatar image URL was invalid or failed to
load, the UI would show a broken image icon.

This commit improves the user experience by displaying a
consistent `_AvatarPlaceholder` widget in all error cases,
including network errors, invalid URLs that resolve to null,
and null user objects.

Fixes: #1558.

Author: vinodsingh-dev-gsoc

.fvmrc

@@ -0,0 +1,3 @@
+{
+  "flutter": "main"
+}

.gitignore

@@ -53,3 +53,6 @@ app.*.map.json
 
 # Old scaffolding hack
 lib/credential_fixture.dart
+
+# FVM Version Cache
+.fvm/

.vscode/settings.json

@@ -1,23 +1,11 @@
-// Visual Studio Code settings for the zulip-flutter repo.
 {
-  // VS Code formats files on save by default.
-  // Like Flutter itself, we don't use the Dart autoformatter,
-  // so disable that VS Code behavior.
   "[dart]": {
-    // This appears redundant with the all-language setting,
-    // but it's not: if the user's personal config has a Dart-specific
-    // setting, then we need a Dart-specific setting to override it.
     "editor.formatOnSave": false,
     "editor.formatOnType": false,
-    "editor.formatOnPaste": false,
+    "editor.formatOnPaste": false
   },
-
-  // For that matter, don't go reformatting whole files in any language.
   "editor.formatOnSave": false,
-
-  // This much more focused automatic fix is helpful, though.
   "files.trimTrailingWhitespace": true,
-
-  // Suppress the warnings that appear for TODOs throughout the codebase.
   "dart.showTodos": false,
-}
+  "dart.flutterSdkPath": ".fvm/versions/main"
+}