fix(portal-self-service): keep dotnet format green under the shared .editorconfig (refs #65)

The imported Nx .editorconfig applied a global 2-space indent + charset=utf-8 to
all files, so dotnet format flagged every 4-space C# line and the BOM'd EF migration.
Scope it: [*.cs] keeps 4-space, and the global charset rule is dropped (utf-8 is the
default; the BOM'd generated migration is left alone). Frontend files stay 2-space.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.editorconfig

@@ -2,12 +2,16 @@
 root = true
 
 [*]
-charset = utf-8
 indent_style = space
 indent_size = 2
 insert_final_newline = true
 trim_trailing_whitespace = true
 
+# .NET sources use 4-space indent (dotnet format enforces this). The 2-space default
+# above is for the frontend (TS/HTML/CSS/JSON); C# keeps the .NET convention.
+[*.cs]
+indent_size = 4
+
 [*.md]
 max_line_length = off
 trim_trailing_whitespace = false