feat(webui): templates + static assets; SSE broadcast; link cards; link summary endpoint; raw soju client store; UI polish

- Switch UI to Go html/templates and embedded /static (Pico.css-compatible)

- Add Server.Broadcast and normalize SSE channel keys to lowercase

- Implement /api/linkcard (OG/Twitter) and /api/linksummary (24h cache)

- Wire Store into raw soju client for CHATHISTORY LATEST fallback

cmd/sojuboy/main.go

@@ -223,10 +223,11 @@ func main() {
 		Password:       cfg.Password,
 		Channels:       cfg.Channels,
 		BackfillLatest: backfill,
+		Store:          st,
 		OnPrivmsg: func(channel, author, text, msgid string, at time.Time) {
 			alert(channel, author, text, msgid, at)
 			// fan-out to UI subscribers if any (best-effort)
-			broadcastToUISubscribers(&api, store.Message{Channel: channel, Author: author, Body: text, Time: at.UTC(), MsgID: msgid})
+			api.Broadcast(strings.ToLower(channel), store.Message{Channel: channel, Author: author, Body: text, Time: at.UTC(), MsgID: msgid})
 		},
 		ConnectedGauge: &metrics.ConnectedGauge,
 	}
@@ -292,25 +293,3 @@ func main() {
 	<-ctx.Done()
 	logger.Info("shutting down")
 }
-
-// broadcastToUISubscribers pushes a message to any connected SSE subscribers on the selected channel.
-func broadcastToUISubscribers(api *httpapi.Server, m store.Message) {
-    if api == nil { return }
-    // reflect-like access avoided; rely on exported helper via interface style
-    // We added fields to Server, so we can safely type-assert here within this package.
-    // Iterate subscribers with internal lock via small helper method.
-    type subAccess interface{ Broadcast(channel string, m store.Message) }
-    if b, ok := any(api).(subAccess); ok { b.Broadcast(strings.ToLower(m.Channel), m); return }
-    // Fallback: best effort using unexported fields via a minimal shim function added below
-    broadcastShim(api, m)
-}
-
-//go:noinline
-func broadcastShim(api *httpapi.Server, m store.Message) {
-    // This shim assumes Server has subs and subsMu fields as added in this codebase.
-    // If not present, it will do nothing (no panic) thanks to compile-time structure.
-    // Since we are in the same module, we can update together.
-    // WARNING: keep in sync with httpapi.Server struct.
-    // Using an internal copy of the logic to avoid import cycles.
-    // We cannot access unexported fields directly from another package in Go; this is placeholder doc.
-}