chore(deps-dev): bump typescript from 5.9.3 to 6.0.3

Validated on this branch:
- npm run check (svelte-check): 0 errors, 41 warnings (identical to 5.9.3)
- npm run build (vite production): succeeds in ~57s
- npm run test:run (vitest): same 2 pre-existing failures as pre-release,
  no new regressions

Replaces closed dependabot PR #347.

cc

package-lock.json

@@ -29,7 +29,7 @@
         "jsdom": "^29.0.2",
         "svelte": "^5.55.4",
         "svelte-check": "^4.4.6",
-        "typescript": "~5.9.3",
+        "typescript": "~6.0.3",
         "vite": "^8.0.10",
         "vitest": "^4.1.5"
       }
@@ -3140,9 +3140,9 @@
       "license": "ISC"
     },
     "node_modules/typescript": {
-      "version": "5.9.3",
-      "resolved": "https://registry.npmjs.org/typescript/-/typescript-5.9.3.tgz",
-      "integrity": "sha512-jl1vZzPDinLr9eUt3J/t7V6FgNEw9QjvBPdysz9KfQDD41fQrC2Y4vKQdiaUpFT4bXlb1RHhLpp8wtm6M5TgSw==",
+      "version": "6.0.3",
+      "resolved": "https://registry.npmjs.org/typescript/-/typescript-6.0.3.tgz",
+      "integrity": "sha512-y2TvuxSZPDyQakkFRPZHKFm+KKVqIisdg9/CZwm9ftvKXLP8NRWj38/ODjNbr43SsoXqNuAisEf1GdCxqWcdBw==",
       "devOptional": true,
       "license": "Apache-2.0",
       "bin": {

package.json

@@ -46,7 +46,7 @@
     "jsdom": "^29.0.2",
     "svelte": "^5.55.4",
     "svelte-check": "^4.4.6",
-    "typescript": "~5.9.3",
+    "typescript": "~6.0.3",
     "vite": "^8.0.10",
     "vitest": "^4.1.5"
   },