feat: replace PrismJS with highlight.js for code syntax highlighting

PrismJS's CJS global state is fundamentally incompatible with Vite's ESM
dev mode, causing missing language support (~40% of dropdown languages)
and fragile loading hacks (optimizeDeps, global assignment).

Replace the entire Prism integration with highlight.js/lib/common which
is ESM-native, has no global state, and covers all 22 dropdown languages
out of the box (~37 common languages included).

Implementation:
- Custom CodeHighlightPlugin using hljs.highlight() for tokenization
- HTML parser extracts flat tokens from hljs output (handles nested spans)
- Token type mapping from hljs scopes to Lexical codeHighlight theme keys
- Selection preservation via absolute character offset save/restore
- Re-entrancy guard prevents infinite transform loops
- Removed @lexical/code-prism import and Vite optimizeDeps workaround

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

bun.lock

@@ -13,6 +13,7 @@
         "@lexical/react": "0.42.0",
         "@lexical/rich-text": "0.42.0",
         "@xyflow/react": "^12.10.1",
+        "highlight.js": "^11.11.1",
         "keytar": "^7.9.0",
         "lexical": "0.42.0",
         "lucide-react": "^0.577.0",
@@ -25,7 +26,6 @@
         "@lexical/headless": "0.42.0",
         "@tailwindcss/vite": "^4.2.2",
         "@types/node": "^25.5.0",
-        "@types/prismjs": "^1.26.6",
         "@types/react": "^19.2.14",
         "@types/react-dom": "^19.2.3",
         "@vitejs/plugin-react": "5.1.0",
@@ -339,8 +339,6 @@
 
     "@types/node": ["@types/node@25.5.0", "", { "dependencies": { "undici-types": "~7.18.0" } }, "sha512-jp2P3tQMSxWugkCUKLRPVUpGaL5MVFwF8RDuSRztfwgN1wmqJeMSbKlnEtQqU8UrhTmzEmZdu2I6v2dpp7XIxw=="],
 
-    "@types/prismjs": ["@types/prismjs@1.26.6", "", {}, "sha512-vqlvI7qlMvcCBbVe0AKAb4f97//Hy0EBTaiW8AalRnG/xAN5zOiWWyrNqNXeq8+KAuvRewjCVY1+IPxk4RdNYw=="],
-
     "@types/react": ["@types/react@19.2.14", "", { "dependencies": { "csstype": "^3.2.2" } }, "sha512-ilcTH/UniCkMdtexkoCN0bI7pMcJDvmQFPvuPvmEaYA/NSfFTAgdUSLAoVjaRJm7+6PvcM+q1zYOwS4wTYMF9w=="],
 
     "@types/react-dom": ["@types/react-dom@19.2.3", "", { "peerDependencies": { "@types/react": "^19.2.0" } }, "sha512-jp2L/eY6fn+KgVVQAOqYItbF0VY/YApe5Mz2F0aykSO8gx31bYCZyvSeYxCHKvzHG5eZjc+zyaS5BrBWya2+kQ=="],
@@ -523,6 +521,8 @@
 
     "hast-util-whitespace": ["hast-util-whitespace@3.0.0", "", { "dependencies": { "@types/hast": "^3.0.0" } }, "sha512-88JUN06ipLwsnv+dVn+OIYOvAuvBMy/Qoi6O7mQHxdPXpjy+Cd6xRkWwux7DKO+4sYILtLBRIKgsdpS2gQc7qw=="],
 
+    "highlight.js": ["highlight.js@11.11.1", "", {}, "sha512-Xwwo44whKBVCYoliBQwaPvtd/2tYFkRQtXDWj1nackaV2JPXx3L0+Jvd8/qCJ2p+ML0/XVkJ2q+Mr+UVdpJK5w=="],
+
     "html-url-attributes": ["html-url-attributes@3.0.1", "", {}, "sha512-ol6UPyBWqsrO6EJySPz2O7ZSr856WDrEzM5zMqp+FJJLGMW35cLYmmZnl0vztAZxRUoNZJFTCohfjuIJ8I4QBQ=="],
 
     "http-cache-semantics": ["http-cache-semantics@4.2.0", "", {}, "sha512-dTxcvPXqPvXBQpq5dUr6mEMJX4oIEFv6bwom3FDwKRDsuIjjJGANqhBuoAn9c1RQJIdAKav33ED65E2ys+87QQ=="],