Make DiagnosticsConfig.severity field private

The severity field should not be public since we provide public API
methods (get_severity and is_enabled) for accessing it. This follows
proper encapsulation patterns already established in the Settings struct.

Changes:
- Make severity field private in DiagnosticsConfig
- Update tests to use get_severity() instead of direct field access
- Maintains proper pub/private boundaries throughout the codebase

Author: claude

crates/djls-conf/src/diagnostics.rs

@@ -60,7 +60,7 @@ pub struct DiagnosticsConfig {
     /// - Prefixes: "S" (all S-series), "T" (all T-series), "S1" (S100-S199)
     /// - More specific patterns override less specific ones
     #[serde(default)]
-    pub severity: HashMap<String, DiagnosticSeverity>,
+    severity: HashMap<String, DiagnosticSeverity>,
 }
 
 impl DiagnosticsConfig {
@@ -273,14 +273,13 @@ mod tests {
         "#;
 
         let config: DiagnosticsConfig = toml::from_str(toml).unwrap();
-        assert_eq!(config.severity.get("S100"), Some(&DiagnosticSeverity::Off));
-        assert_eq!(
-            config.severity.get("S101"),
-            Some(&DiagnosticSeverity::Warning)
-        );
-        assert_eq!(config.severity.get("S102"), Some(&DiagnosticSeverity::Hint));
-        assert_eq!(config.severity.get("T"), Some(&DiagnosticSeverity::Off));
-        assert_eq!(config.severity.get("T100"), Some(&DiagnosticSeverity::Info));
+        assert_eq!(config.get_severity("S100"), DiagnosticSeverity::Off);
+        assert_eq!(config.get_severity("S101"), DiagnosticSeverity::Warning);
+        assert_eq!(config.get_severity("S102"), DiagnosticSeverity::Hint);
+        // T prefix applies to T900
+        assert_eq!(config.get_severity("T900"), DiagnosticSeverity::Off);
+        // T100 has specific override
+        assert_eq!(config.get_severity("T100"), DiagnosticSeverity::Info);
     }
 
     #[test]

crates/djls-conf/src/lib.rs

@@ -298,21 +298,24 @@ T100 = "hint"
             )
             .unwrap();
             let settings = Settings::new(Utf8Path::from_path(dir.path()).unwrap(), None).unwrap();
+            // Test via public API
             assert_eq!(
-                settings.diagnostics.severity.get("S100"),
-                Some(&DiagnosticSeverity::Off)
+                settings.diagnostics.get_severity("S100"),
+                DiagnosticSeverity::Off
             );
             assert_eq!(
-                settings.diagnostics.severity.get("S101"),
-                Some(&DiagnosticSeverity::Warning)
+                settings.diagnostics.get_severity("S101"),
+                DiagnosticSeverity::Warning
             );
+            // T prefix applies to T900
             assert_eq!(
-                settings.diagnostics.severity.get("T"),
-                Some(&DiagnosticSeverity::Off)
+                settings.diagnostics.get_severity("T900"),
+                DiagnosticSeverity::Off
             );
+            // T100 has specific override
             assert_eq!(
-                settings.diagnostics.severity.get("T100"),
-                Some(&DiagnosticSeverity::Hint)
+                settings.diagnostics.get_severity("T100"),
+                DiagnosticSeverity::Hint
             );
         }
     }