feat(info): show the install reason and drop the indentation

N? and `info PKG` now print three lines, none indented:

    PKG: <description>
    reason: explicitly installed | installed as a dependency | unknown | not installed
    required by: <installed dependents, comma separated> | nothing

The reason comes from a new <be>_reason backend function: apt-mark
showauto / showmanual (dpkg decides for a package in neither list), the
Install Reason of pacman -Qi, dnf repoquery --installed %{reason} (dnf4
and dnf5 words) and the Installed line of zypper info (rpm plus libzypp's
AutoInstalled when zypper is locked). A row whose old version is "-" is
not installed and the backend is not asked. The "(installed)" qualifier
moves to --help, README and DESIGN.

The rpm E2E fixture and e2e_reset now also mark su-dummy-a and su-dummy-c
as user-installed on dnf, which records plain rpm installs as "unknown",
so 1? and 2? show both reasons on all 12 distros. The verified commands
are recorded in discovery/{apt,pacman,rpm}.md.

tests/unit/fakes/zypper/zypper

@@ -6,6 +6,8 @@
 # FAKE_ZYPPER_DUP=fixture|empty|removes the `dist-upgrade --dry-run` plan (data/zypper/dup-*.xml).
 # addlock writes real zypp lock entries into the locksfile.path of $ZYPP_CONF (default
 # /etc/zypp/locks is never touched: the fake refuses); update/dist-upgrade log that file.
+# info replays data/zypper/info-NAME.txt (exit 104 without one); FAKE_ZYPPER_INFO_RC=7 makes it fail
+# like a zypp lock held by another process.
 # shellcheck source=../fakelib.bash
 . "${BASH_SOURCE[0]%/*}/../fakelib.bash"
 fake_log "${ZYPP_CONF:+ZYPP_CONF=$ZYPP_CONF }$*"
@@ -43,6 +45,11 @@ refresh)
 list-updates) cat "$D/lu-${FAKE_ZYPPER_LU:-fixture}.xml" ;;
 info)
 	p=${args[-1]}
+	if [[ -n ${FAKE_ZYPPER_INFO_RC:-} ]]; then
+		echo "System management is locked by the application with pid 4242 (zypper)."
+		echo "Close this application before trying again."
+		exit "$FAKE_ZYPPER_INFO_RC"
+	fi
 	if [[ -f $D/info-$p.txt ]]; then cat "$D/info-$p.txt"; else
 		echo "package '$p' not found."
 		exit 104