feat: message reactions + link/image previews

Reactions (full stack):
- Wire: MsgReaction peer message (reaction_mid, reaction_emoji)
- Store: reactions table (mid, emoji, from_peer), SaveReaction, ReactionsForRoom
- Daemon: CmdSendReaction IPC command; EvtReaction IPC event; stored reactions
  replayed to newly-connected IPC clients alongside history
- Web UI: reactions state (mid → emoji → [fromId]); hover a message to reveal
  a + button; click opens a 6-emoji picker (👍❤️😂😮😢🙏); reaction chips
  appear below the message with count and tooltip; own reactions highlighted

Link/image previews:
- URLs in message text rendered as clickable <a> links
- Image URLs (.jpg/.jpeg/.png/.gif/.webp/blob:/data:image) rendered as inline
  thumbnails (max 320×200px) below the link

Also scoped push notifications architecture in FUTURE.md.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

internal/ipc/ipc.go

@@ -244,6 +244,34 @@ func handleClient(conn net.Conn, mgr *netmgr.Manager) {
 				})
 			}
 
+		case proto.CmdSendReaction:
+			n := mgr.Resolve(cmd.NetworkID)
+			if n == nil {
+				send(errMsg("send_reaction: not joined to any network"))
+				continue
+			}
+			if cmd.ReactionMID == "" || cmd.ReactionEmoji == "" {
+				send(errMsg("send_reaction: reaction_mid and reaction_emoji are required"))
+				continue
+			}
+			wire, err := json.Marshal(proto.PeerMessage{
+				Type:          proto.MsgReaction,
+				ReactionMID:   cmd.ReactionMID,
+				ReactionEmoji: cmd.ReactionEmoji,
+			})
+			if err != nil {
+				continue
+			}
+			n.Mesh.Broadcast(wire)
+			n.Mesh.SaveReaction(cmd.ReactionMID, cmd.ReactionEmoji, string(n.Identity.PeerID()))
+			n.Mesh.Emit(proto.IpcMessage{
+				Type:          proto.EvtReaction,
+				NetworkID:     n.ID,
+				PeerID:        ptr(n.Identity.PeerID()),
+				ReactionMID:   cmd.ReactionMID,
+				ReactionEmoji: cmd.ReactionEmoji,
+			})
+
 		case proto.CmdCreateRoom:
 			n := mgr.Resolve(cmd.NetworkID)
 			if n == nil {
@@ -505,6 +533,25 @@ func sendStoredHistory(mgr *netmgr.Manager, send func(proto.IpcMessage)) {
 			Room:      room,
 			Messages:  msgs,
 		})
+		// Send stored reactions for this room's messages.
+		rxns, err := n.Store.ReactionsForRoom(room)
+		if err != nil {
+			continue
+		}
+		for mid, byEmoji := range rxns {
+			for emoji, fromPeers := range byEmoji {
+				for _, fromPeer := range fromPeers {
+					pid := proto.PeerID(fromPeer)
+					send(proto.IpcMessage{
+						Type:          proto.EvtReaction,
+						NetworkID:     n.ID,
+						PeerID:        &pid,
+						ReactionMID:   mid,
+						ReactionEmoji: emoji,
+					})
+				}
+			}
+		}
 	}
 }