fix(bootstrap): refuse an unbracketed ipv6 nano listen address

validate_listen checked only the port, so FELIS_NANO_LISTEN=::1:8081
passed. Go refuses that form ("too many colons in address") and needs
[::1]:8081, so the unit crash-looped on every start. A host part that
contains a colon must now be in brackets.

With that, the bare ::1 pattern in nano_listen_is_loopback can no
longer match an address that gets this far, so it goes. [::1] stays.
The harness adds ::1:8081 to the refused addresses, and [::]:8081 and
:8081, both of which Go binds, to the accepted ones.

deploy/bootstrap_test.sh

@@ -295,10 +295,10 @@ check_listen() { # value
     validate_listen FELIS_NANO_LISTEN "$1" && echo VALID' _ "$1" 2>&1
 }
 
-for v in 8081 127.0.0.1 127.0.0.1:0 127.0.0.1:65536 127.0.0.1:x; do
+for v in 8081 127.0.0.1 127.0.0.1:0 127.0.0.1:65536 127.0.0.1:x ::1:8081; do
   expect "listen address $v is refused" "DIE: FELIS_NANO_LISTEN" "$(check_listen "$v")"
 done
-for v in '[::1]:8081' 0.0.0.0:8081 127.0.0.1:8081; do
+for v in '[::1]:8081' '[::]:8081' :8081 0.0.0.0:8081 127.0.0.1:8081; do
   expect "listen address $v is accepted" VALID "$(check_listen "$v")"
 done