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/mesh/mesh.go

@@ -146,6 +146,17 @@ func (m *Mesh) AddPeer(conn *PeerConn) {
 	})
 }
 
+// SaveReaction persists a reaction if a store is configured.
+// Duplicate (mid, emoji, fromPeer) triples are silently dropped.
+func (m *Mesh) SaveReaction(mid, emoji, fromPeer string) {
+	if m.Store == nil {
+		return
+	}
+	if err := m.Store.SaveReaction(mid, emoji, fromPeer); err != nil {
+		log.Printf("mesh: store reaction %s/%s: %v", mid, emoji, err)
+	}
+}
+
 // SaveMessage persists a chat message if a store is configured.
 // Duplicate mids are silently dropped.
 func (m *Mesh) SaveMessage(msg *proto.ChatMessage) {

internal/mesh/peer.go

@@ -307,6 +307,18 @@ func dispatchPeerMessage(msg proto.PeerMessage, from proto.PeerID, m *Mesh) {
 	case proto.MsgHistoryChunk:
 		go m.HandleHistoryChunk(msg.Room, msg.History)
 
+	case proto.MsgReaction:
+		if msg.ReactionMID == "" || msg.ReactionEmoji == "" {
+			return
+		}
+		m.SaveReaction(msg.ReactionMID, msg.ReactionEmoji, string(from))
+		m.emit(proto.IpcMessage{
+			Type:          proto.EvtReaction,
+			PeerID:        peerIDPtr(from),
+			ReactionMID:   msg.ReactionMID,
+			ReactionEmoji: msg.ReactionEmoji,
+		})
+
 	case proto.MsgPing:
 		log.Printf("mesh: ping from %s", from.Short())
 	case proto.MsgPong: