Scaffold Svelte frontend and browser test matrix

Establish the TypeScript 7, Oxlint, Vitest, and Playwright workspace with an isolated Svelte diagnostics compatibility boundary.

web/.oxlintrc.json

@@ -0,0 +1,17 @@
+{
+  "$schema": "./node_modules/oxlint/configuration_schema.json",
+  "categories": {
+    "correctness": "error",
+    "suspicious": "error"
+  },
+  "ignorePatterns": ["node_modules/**", "tools/**"],
+  "options": {
+    "typeAware": true
+  },
+  "plugins": ["typescript", "vitest"],
+  "rules": {
+    "typescript/await-thenable": "error",
+    "typescript/no-floating-promises": "error",
+    "typescript/no-misused-promises": "error"
+  }
+}