Render search suggestions on the server

The typeahead requests /_search via htmx (debounced, newer requests
replace in-flight ones) and gets rendered rows with the match
highlighting done in Go. Rows are links, so picking in the header is
plain navigation; the editor's link dialog reads data-name instead. The
editor's [[ autocomplete keeps the JSON response.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

suggest_test.go

@@ -0,0 +1,21 @@
+package main
+
+import "testing"
+
+func TestHighlightMatches(t *testing.T) {
+	cases := []struct{ name, query, want string }{
+		{"Project Alpha", "alpha", "Project <strong>Alpha</strong>"},
+		// Overlapping and adjacent spans merge.
+		{"Project Alpha", "pro ject", "<strong>Project</strong> Alpha"},
+		{"Project Alpha", "roj proj", "<strong>Proj</strong>ect Alpha"},
+		{"a<b>&c", "b", "a&lt;<strong>b</strong>&gt;&amp;c"},
+		{"Notes", "zzz", "Notes"},
+		// Lowercasing changes the byte length: no highlight, still escaped.
+		{"İstanbul <x>", "stan", "İstanbul &lt;x&gt;"},
+	}
+	for _, c := range cases {
+		if got := string(highlightMatches(c.name, suggestTokens(c.query))); got != c.want {
+			t.Errorf("highlightMatches(%q, %q) = %q, want %q", c.name, c.query, got, c.want)
+		}
+	}
+}