controller_cli: readline, discovery integration, peers/connect commands

- readline replaces fgets — line editing and command history
- Discovery runs at startup (always); discovered peers print inline as they appear
- --host is now optional; without it, starts in discovery-only mode
- New REPL commands:
    peers              list discovered nodes with index
    connect            connect to first discovered peer
    connect <idx>      connect to peer by index
    connect <host:port> connect directly
- connect switching closes the old connection before opening the new one
- Commands that require a connection print "not connected" when conn is NULL
- Makefile: add $(DISCOVERY_OBJ) and -lreadline to controller_cli link

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

dev/cli/Makefile

@@ -109,8 +109,8 @@ $(CLI_BUILD)/stream_recv_cli: $(CLI_BUILD)/stream_recv_cli.o $(COMMON_OBJ) $(SER
 $(CLI_BUILD)/reconciler_cli: $(CLI_BUILD)/reconciler_cli.o $(RECONCILER_OBJ)
 	$(CC) $(CFLAGS) -o $@ $^
 
-$(CLI_BUILD)/controller_cli: $(CLI_BUILD)/controller_cli.o $(COMMON_OBJ) $(SERIAL_OBJ) $(TRANSPORT_OBJ) $(PROTOCOL_OBJ)
-	$(CC) $(CFLAGS) -o $@ $^ -lpthread
+$(CLI_BUILD)/controller_cli: $(CLI_BUILD)/controller_cli.o $(COMMON_OBJ) $(SERIAL_OBJ) $(TRANSPORT_OBJ) $(DISCOVERY_OBJ) $(PROTOCOL_OBJ)
+	$(CC) $(CFLAGS) -o $@ $^ -lpthread -lreadline
 
 $(CLI_BUILD):
 	mkdir -p $@