search: make the navigation form work from every page (AUD-151)

The nav form carried hx-get="/search" hx-target="#search-results", but
#search-results exists only on /search. On every other page htmx found no
target and silently discarded the response: a search box that looks like it
works and does nothing.

- SearchForm is now a plain GET with no htmx attributes (navigation and the
  landing page), so it navigates to /search?q=… from any page and with
  JavaScript disabled.
- SearchFormLive keeps the in-place swap on the search page, where the target
  does exist. For HX-Request the server now returns the block's *contents*
  (SearchResultsBody), so the fragment no longer nests a second element with
  id="search-results" inside the live region.
- Empty query shows a prompt instead of an empty list. A zero-match query says
  "Nothing found" and offers the six areas plus the evidence index.
- The result count is role="status" inside the existing aria-live container, so
  a screen reader reads "4 results for …" rather than a run of titles.

Tests (internal/server, internal/site):
- the nav form carries no htmx attribute on nine pages, and no built page
  carries an hx-target whose element is missing (walks all of dist/);
- search submitted from /, /edge/ and /platform/ lands on a page with results
  with no HX-Request header, i.e. the JavaScript-disabled path;
- empty query, zero match and the announced count;
- a content change followed by a build is visible in dist/search.db. That is
  the deploy path: deploy/deploy.sh runs `make dist` before it stages a
  release, and search.Build removes and rewrites the index every build.

DoD: search from home, /edge and /platform lands on results; works with
JavaScript disabled; zero-match query shows a message; content change followed
by a deploy is reflected in search; no htmx request targets a missing element.

(cherry picked from commit a56c795768e1e9b10204aae04c3612d7a96775a7)

internal/site/site_test.go

@@ -7,6 +7,7 @@ import (
 	"testing"
 
 	"gitea.lab.audasmedia.com.au/sam/ai-resume/internal/content"
+	"gitea.lab.audasmedia.com.au/sam/ai-resume/internal/search"
 )
 
 // newSite loads the repository's own content. If this fails, every other test
@@ -172,3 +173,93 @@ func TestBuildWritesEveryPublishedPage(t *testing.T) {
 		}
 	}
 }
+
+// copyTree copies a directory tree. The freshness test needs its own content
+// tree so it can change a page without touching the repository.
+func copyTree(src, dst string) error {
+	return filepath.WalkDir(src, func(p string, d os.DirEntry, err error) error {
+		if err != nil {
+			return err
+		}
+		rel, err := filepath.Rel(src, p)
+		if err != nil {
+			return err
+		}
+		target := filepath.Join(dst, rel)
+		if d.IsDir() {
+			return os.MkdirAll(target, 0o755)
+		}
+		raw, err := os.ReadFile(p)
+		if err != nil {
+			return err
+		}
+		return os.WriteFile(target, raw, 0o644)
+	})
+}
+
+// TestSearchIndexFollowsContent is the AUD-151 freshness line: a content change
+// followed by a build is reflected in search. The deploy path is exactly this —
+// deploy/deploy.sh runs `make dist` before it stages a release, and the build
+// rewrites dist/search.db from content/ every time (search.Build removes the old
+// file), so search can never serve an index from a previous content tree.
+func TestSearchIndexFollowsContent(t *testing.T) {
+	root, err := filepath.Abs("../..")
+	if err != nil {
+		t.Fatal(err)
+	}
+	dir := t.TempDir()
+	contentDir := filepath.Join(dir, "content")
+	if err := copyTree(filepath.Join(root, "content"), contentDir); err != nil {
+		t.Fatalf("copy content: %v", err)
+	}
+	out := filepath.Join(dir, "dist")
+
+	build := func() {
+		t.Helper()
+		s, err := New(Config{Root: root, ContentDir: contentDir, OutDir: out})
+		if err != nil {
+			t.Fatalf("load site: %v", err)
+		}
+		if err := s.Build(); err != nil {
+			t.Fatalf("build: %v", err)
+		}
+	}
+	query := func(q string) []search.Result {
+		t.Helper()
+		idx, err := search.Open(filepath.Join(out, IndexFile))
+		if err != nil {
+			t.Fatalf("open index: %v", err)
+		}
+		defer idx.Close()
+		results, err := idx.Query(q, 20)
+		if err != nil {
+			t.Fatalf("query %q: %v", q, err)
+		}
+		return results
+	}
+
+	const token = "kumquatprotocol"
+	build()
+	if got := query(token); len(got) != 0 {
+		t.Fatalf("token is already indexed in %d results; the test proves nothing", len(got))
+	}
+
+	page := filepath.Join(contentDir, "edge", "edge-fleet.md")
+	raw, err := os.ReadFile(page)
+	if err != nil {
+		t.Fatal(err)
+	}
+	added := string(raw) + "\n\nA " + token + " harness keeps the nodes in step.\n"
+	if err := os.WriteFile(page, []byte(added), 0o644); err != nil {
+		t.Fatal(err)
+	}
+
+	build()
+	results := query(token)
+	if len(results) == 0 {
+		t.Fatal("content change is not in the rebuilt index")
+	}
+	if results[0].URL != "/edge/edge-fleet/" {
+		t.Errorf("token found at %s, want /edge/edge-fleet/", results[0].URL)
+	}
+}