refactor(types): replace unsafe explicit type casting and JSON map casts with pattern-matching validation #1510

Summary

A static search across lib/ identified 245 unchecked explicit casts (as Map, as List, as String, etc.).

Most notably, in lib/core/extensions/local_extension_registry.dart:57:

final json = jsonDecode(content) as Map<String, dynamic>;

If a manifest file on disk contains a JSON array ([...]), a primitive value, or invalid formatting, this throws an unhandled TypeError at runtime (List<dynamic> is not a subtype of type Map<String, dynamic>).

Similarly, in lib/core/team/team_profile.dart (lines 129–137) and lib/core/erd/erd_saved_layout.dart (lines 172–181), values extracted from untyped maps are cast directly via item['field'] as String? without validating against corrupt database records.

Proposed Solution

1. Use Dart 3 pattern-matching type guards for JSON deserialization:

   final decoded = jsonDecode(content);
   if (decoded is! Map<String, dynamic>) {
     throw FormatException('Expected JSON object, got ${decoded.runtimeType}');
   }

2. Introduce a safe map extraction helper (e.g. asStringOrNull(), asIntOrNull()) for config/profile parsing.
3. Replace raw as List<dynamic> casts with List<dynamic>.from(...) or typed collection checks.

Acceptance Criteria

• Corrupted or unexpected JSON manifests / layout files produce clear diagnostic errors rather than unhandled TypeError crashes.
• Safe type extraction helpers are used across extension and profile deserializers.