fix(highlight): highlight Svelte components (#3487)

* fix(highlight): highlight Svelte components

`.svelte` had no entry in the extension table, so `highlightCode` fell through
to one unstyled token per line. That is the same table the file pane, the diff
tokens, markdown fences and the web editor all resolve through, so a component
rendered as plain text everywhere in the app.

Register `@replit/codemirror-lang-svelte`. Its `svelteLanguage` already wires
the mixed parsing for the `<script>` and `<style>` blocks, so the script gets
JS/TS roles, the style block gets CSS roles, and the template gets tag,
directive and mustache roles. It comes from the same publisher as the
`@replit/codemirror-lang-csharp` entry already in this package, and only the
grammar itself is declared: its CodeMirror peers resolve the same way the C#
grammar's peers already do.

* test(server): cover Svelte diff highlighting

The review surface in the issue is the diff, and the daemon is what tokenizes
it (`diff-highlighter.ts` calls `highlightCode`), so the regression belongs
here too: script, template block and markup roles on a `.svelte` hunk.

package-lock.json

@@ -2573,6 +2573,54 @@
         "@lezer/common": "^1.1.0"
       }
     },
+    "node_modules/@codemirror/lang-css": {
+      "version": "6.3.1",
+      "resolved": "https://registry.npmjs.org/@codemirror/lang-css/-/lang-css-6.3.1.tgz",
+      "integrity": "sha512-kr5fwBGiGtmz6l0LSJIbno9QrifNMUusivHbnA1H6Dmqy4HZFte3UAICix1VuKo0lMPKQr2rqB+0BkKi/S3Ejg==",
+      "license": "MIT",
+      "peer": true,
+      "dependencies": {
+        "@codemirror/autocomplete": "^6.0.0",
+        "@codemirror/language": "^6.0.0",
+        "@codemirror/state": "^6.0.0",
+        "@lezer/common": "^1.0.2",
+        "@lezer/css": "^1.1.7"
+      }
+    },
+    "node_modules/@codemirror/lang-html": {
+      "version": "6.4.12",
+      "resolved": "https://registry.npmjs.org/@codemirror/lang-html/-/lang-html-6.4.12.tgz",
+      "integrity": "sha512-pw2ReWKUqSkbvh76RAT4NYxiogRu+PWkR2ukAwO9uOgrm8uipkzjtKKtNpyeAQwHOqxEeSvAXZ6vr3AfyB9y/w==",
+      "license": "MIT",
+      "peer": true,
+      "dependencies": {
+        "@codemirror/autocomplete": "^6.0.0",
+        "@codemirror/lang-css": "^6.0.0",
+        "@codemirror/lang-javascript": "^6.0.0",
+        "@codemirror/language": "^6.4.0",
+        "@codemirror/state": "^6.0.0",
+        "@codemirror/view": "^6.17.0",
+        "@lezer/common": "^1.0.0",
+        "@lezer/css": "^1.1.0",
+        "@lezer/html": "^1.3.12"
+      }
+    },
+    "node_modules/@codemirror/lang-javascript": {
+      "version": "6.2.5",
+      "resolved": "https://registry.npmjs.org/@codemirror/lang-javascript/-/lang-javascript-6.2.5.tgz",
+      "integrity": "sha512-zD4e5mS+50htS7F+TYjBPsiIFGanfVqg4HyUz6WNFikgOPf2BgKlx+TQedI1w6n/IqRBVBbBWmGFdLB/7uxO4A==",
+      "license": "MIT",
+      "peer": true,
+      "dependencies": {
+        "@codemirror/autocomplete": "^6.0.0",
+        "@codemirror/language": "^6.6.0",
+        "@codemirror/lint": "^6.0.0",
+        "@codemirror/state": "^6.0.0",
+        "@codemirror/view": "^6.17.0",
+        "@lezer/common": "^1.0.0",
+        "@lezer/javascript": "^1.0.0"
+      }
+    },
     "node_modules/@codemirror/language": {
       "version": "6.12.4",
       "resolved": "https://registry.npmjs.org/@codemirror/language/-/language-6.12.4.tgz",
@@ -2596,6 +2644,18 @@
         "@codemirror/language": "^6.0.0"
       }
     },
+    "node_modules/@codemirror/lint": {
+      "version": "6.9.7",
+      "resolved": "https://registry.npmjs.org/@codemirror/lint/-/lint-6.9.7.tgz",
+      "integrity": "sha512-28/+iWLYxKxsvGYhSYL7zaCZqLz5+FFFDq9tVsvGv9kv8RY4fFAchJ5WX9M3YrrRlTIsECjsXPqeNgnSmNP2dg==",
+      "license": "MIT",
+      "peer": true,
+      "dependencies": {
+        "@codemirror/state": "^6.0.0",
+        "@codemirror/view": "^6.42.0",
+        "crelt": "^1.0.5"
+      }
+    },
     "node_modules/@codemirror/search": {
       "version": "6.7.1",
       "resolved": "https://registry.npmjs.org/@codemirror/search/-/search-6.7.1.tgz",
@@ -11169,6 +11229,25 @@
         "@lezer/lr": "^1.0.0"
       }
     },
+    "node_modules/@replit/codemirror-lang-svelte": {
+      "version": "6.0.0",
+      "resolved": "https://registry.npmjs.org/@replit/codemirror-lang-svelte/-/codemirror-lang-svelte-6.0.0.tgz",
+      "integrity": "sha512-U2OqqgMM6jKelL0GNWbAmqlu1S078zZNoBqlJBW+retTc5M4Mha6/Y2cf4SVg6ddgloJvmcSpt4hHrVoM4ePRA==",
+      "license": "MIT",
+      "peerDependencies": {
+        "@codemirror/autocomplete": "^6.0.0",
+        "@codemirror/lang-css": "^6.0.1",
+        "@codemirror/lang-html": "^6.2.0",
+        "@codemirror/lang-javascript": "^6.1.1",
+        "@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/javascript": "^1.2.0",
+        "@lezer/lr": "^1.0.0"
+      }
+    },
     "node_modules/@replit/codemirror-vim": {
       "version": "6.3.0",
       "resolved": "https://registry.npmjs.org/@replit/codemirror-vim/-/codemirror-vim-6.3.0.tgz",
@@ -38597,6 +38676,7 @@
         "@lezer/yaml": "^1.0.4",
         "@replit/codemirror-lang-csharp": "^6.2.0",
         "@replit/codemirror-lang-nix": "^6.0.1",
+        "@replit/codemirror-lang-svelte": "^6.0.0",
         "lezer-elixir": "^1.1.2"
       },
       "devDependencies": {