feat: add C# syntax highlighting (#1651)

Wire the @replit/codemirror-lang-csharp Lezer grammar into @getpaseo/highlight following the existing per-language pattern (Java/Rust/Swift). Map the cs extension to the parser and alias the csharp and c# markdown fence names so fenced code blocks highlight.

Register csharpLanguage.parser rather than the package's raw parser export: the highlight styleTags are applied only inside csharpLanguage (via parser.configure), so the raw parser would parse but render unstyled.

Closes #1527

Co-authored-by: Clemens Wagner <wagner.clemens@gmx.de>
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

package-lock.json

@@ -11166,6 +11166,21 @@
         "nanoid": "^3.3.11"
       }
     },
+    "node_modules/@replit/codemirror-lang-csharp": {
+      "version": "6.2.0",
+      "resolved": "https://registry.npmjs.org/@replit/codemirror-lang-csharp/-/codemirror-lang-csharp-6.2.0.tgz",
+      "integrity": "sha512-6utbaWkoymhoAXj051mkRp+VIJlpwUgCX9Toevz3YatiZsz512fw3OVCedXQx+WcR0wb6zVHjChnuxqfCLtFVQ==",
+      "license": "MIT",
+      "peerDependencies": {
+        "@codemirror/autocomplete": "^6.0.0",
+        "@codemirror/language": "^6.0.0",
+        "@codemirror/state": "^6.0.0",
+        "@codemirror/view": "^6.0.0",
+        "@lezer/common": "^1.0.0",
+        "@lezer/highlight": "^1.0.0",
+        "@lezer/lr": "^1.0.0"
+      }
+    },
     "node_modules/@rollup/pluginutils": {
       "version": "5.3.0",
       "resolved": "https://registry.npmjs.org/@rollup/pluginutils/-/pluginutils-5.3.0.tgz",
@@ -36989,6 +37004,7 @@
         "@lezer/rust": "^1.0.2",
         "@lezer/xml": "^1.0.6",
         "@lezer/yaml": "^1.0.4",
+        "@replit/codemirror-lang-csharp": "^6.2.0",
         "lezer-elixir": "^1.1.2"
       },
       "devDependencies": {