fix(search): register the headerSearch Alpine component (dropdown regression)

The dropdown never opened on typing: the search-dropdown migration left
./search un-imported after dropping the initializeSearch call from
header.ts, so the bundler tree-shook the module away and the
x-data="headerSearch" scope never registered — every handler binding
(input/focus/keys) silently died. This is a client-wiring defect that
HTTP-level integration tests structurally cannot see; a Playwright e2e
spec (e2e/search-scrubber.spec.ts) now drives the real bundle: sub-2-char
input stays closed, 2+ chars opens the swapped templ dropdown.

web/src/header.ts

@@ -1,4 +1,9 @@
 import { Alpine } from "./alpine";
+// Side-effect import: registers the headerSearch Alpine component that
+// owns the header dropdown's client-local state (open/close/keyboard).
+// Without it the bundler tree-shakes the module away and the search
+// input silently stops opening the dropdown.
+import "./search";
 import {
   initializeTheme,
   changeTheme,