Embedded the frontend in the binary, and built it in the build script

`npm run sync` in web/ copies the build output (web/dist, from npm run build)
to internal/frontend/dist, which the binary embeds. Go can't embed from
outside the package's directory (web/ is also outside the Go module), hence
the copy. Only dist/.gitkeep is committed, so a fresh clone still compiles,
and a binary built without syncing first serves no frontend.

job-search serve serves server.frontend.dir if it is set, or else the
embedded build, or warns that there is no frontend. scripts/build.sh builds
and syncs the frontend before building, running npm ci first for a release
or when web/node_modules is missing.

web/package.json

@@ -12,7 +12,8 @@
     "format": "prettier --write .",
     "format:check": "prettier --check .",
     "check": "npm run typecheck && npm run lint && npm run format:check",
-    "generate:api": "node scripts/generateApiTypes.ts"
+    "generate:api": "node scripts/generateApiTypes.ts",
+    "sync": "node scripts/syncDist.ts"
   },
   "dependencies": {
     "solid-js": "^1.9.3"