chore(deps): typescript 5→6, @types/node 22→25, esbuild 0.25→0.28

All three were drop-in within the major-version range; the only
required code change was adding `src/types/css.d.ts` to declare the
`*.css` side-effect import shape (TypeScript 6 stopped silently
accepting unknown side-effect imports).

Tests: 1185/1185 vitest. tsc clean. build:worker clean.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

package.json

@@ -107,7 +107,7 @@
     "@types/archiver": "^7.0.0",
     "@types/iso-3166-2": "^1.0.4",
     "@types/mailparser": "^3.4.6",
-    "@types/node": "22",
+    "@types/node": "^25.6.2",
     "@types/nodemailer": "^8.0.0",
     "@types/react": "^19.2.14",
     "@types/react-dom": "^19.2.3",
@@ -115,7 +115,7 @@
     "autoprefixer": "^10.5.0",
     "dotenv": "^17.4.2",
     "drizzle-kit": "^0.31.10",
-    "esbuild": "^0.25.12",
+    "esbuild": "^0.28.0",
     "eslint": "^9.39.4",
     "eslint-config-next": "15.5.18",
     "eslint-config-prettier": "^10.1.8",
@@ -126,7 +126,7 @@
     "react-grab": "^0.1.33",
     "tailwindcss": "^3.4.19",
     "tsx": "^4.21.0",
-    "typescript": "^5.9.3",
+    "typescript": "^6.0.3",
     "vitest": "^4.1.5"
   }
 }