Make the client typecheck runnable (vitest/vite ambient types)

The client had no `typecheck` script and tsc couldn't even start (the
baseUrl deprecation errored out, same as server/shared already silence).
Add `ignoreDeprecations: "6.0"` to match the other workspaces, a `typecheck`
npm script, and a src/vite-env.d.ts referencing vite/client + vitest/globals
so tsc knows the test globals (describe/it/expect/vi). This turns ~3600
phantom "Cannot find name" errors into a real, measurable count (~590 actual
type errors remain, to be worked down). Type-only; no runtime change.

client/package.json

@@ -8,6 +8,7 @@
     "prebuild": "node scripts/generate-icons.mjs",
     "build": "vite build",
     "preview": "vite preview",
+    "typecheck": "tsc --noEmit",
     "test": "vitest run",
     "test:unit": "vitest run tests/unit",
     "test:integration": "vitest run tests/integration src/**/*.test.{ts,tsx}",

client/src/vite-env.d.ts

@@ -0,0 +1,2 @@
+/// <reference types="vite/client" />
+/// <reference types="vitest/globals" />

client/tsconfig.json

@@ -8,6 +8,7 @@
     "moduleResolution": "bundler",
     "allowImportingTsExtensions": true,
     "baseUrl": ".",
+    "ignoreDeprecations": "6.0",
     "paths": {
       "@trek/shared": ["../shared/src/index.ts"],
       "@trek/shared/*": ["../shared/src/*"]