chore(web): declare unified/remark-parse/remark-rehype/hast-util-to-html

The new markdown-text regression test imports these directly to drive the
unified pipeline end-to-end. They were resolving via transitive deps from
remark-math and rehype-katex, which is fragile — a future dep upgrade can
remove the transitives and break the test.

Declare them explicitly under devDependencies. No code change; lockfile
records the same versions that were already installed transitively
(unified@11.0.5, remark-parse@11.0.0, remark-rehype@11.1.2,
hast-util-to-html@9.0.5).

Addresses the HAPI Bot review finding on PR tiann#805.

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: heavygee

bun.lock

@@ -57,10 +57,14 @@
         "@tailwindcss/postcss": "^4.1.18",
         "@vitejs/plugin-react": "^5.1.2",
         "autoprefixer": "^10.4.23",
+        "hast-util-to-html": "^9.0.5",
         "jsdom": "^26.1.0",
         "postcss": "^8.5.6",
+        "remark-parse": "^11.0.0",
+        "remark-rehype": "^11.1.2",
         "tailwindcss": "^4.1.18",
         "typescript": "^5.9.3",
+        "unified": "^11.0.5",
         "vite": "^7.3.0",
         "vitest": "^4.0.16"
     }