build: add client-side TypeScript compilation pipeline

Adds scripts/build-client.mjs which uses esbuild to compile TypeScript
files in src/scripts/client/ into minified IIFE bundles, then writes
them as TypeScript string-constant modules in src/scripts/generated/.

- Adds build:client npm script; wires it as prebuild and predev hooks
- Adds src/scripts/client/tsconfig.json with DOM lib for IDE support
- Excludes src/scripts/client/ from the root Worker tsconfig to avoid
  DOM type conflicts with the Cloudflare Workers runtime types

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/scripts/client/tsconfig.json

@@ -0,0 +1,10 @@
+{
+  "extends": "../../../tsconfig.json",
+  "compilerOptions": {
+    "lib": ["ES2021", "DOM"],
+    "types": [],
+    "noEmit": true
+  },
+  "include": ["./**/*"],
+  "exclude": []
+}