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/dnf/dnf

@@ -5,7 +5,9 @@
 # fake dnf (unit tests). FAKE_DNF_MAJOR=4|5 picks the output dialect; FAKE_DNF_CHECK_RC=0|1 simulates
 # "no updates" / an error; FAKE_DNF_CHECK=obsoletes replays a check-update with only an
 # "Obsoleting Packages" section; FAKE_DNF_REMOVE_REFUSE=1 makes `--assumeno remove` fail;
-# removal tables: see the --assumeno remove branch.
+# removal tables: see the --assumeno remove branch. `repoquery --installed --qf %{reason}`: REASON of
+# data/rpm/db.bash (dnf5's words with FAKE_DNF_MAJOR=5), FAKE_DNF_REASON="pkg=raw value" overrides
+# it, FAKE_DNF_REPOQUERY_RC=N makes repoquery fail.
 # shellcheck source=../fakelib.bash
 . "${BASH_SOURCE[0]%/*}/../fakelib.bash"
 # shellcheck source=../../data/rpm/db.bash
@@ -41,7 +43,28 @@ case " $* " in
 	;;
 *' repoquery '*)
 	p=${pos[-1]}
+	rc=$(fake_rc FAKE_DNF_REPOQUERY_RC 0)
+	if ((rc)); then
+		echo "Error: rpmdb open failed" >&2
+		exit "$rc"
+	fi
 	case " $* " in
+	*' --installed '*'%{reason}'*)
+		installed "$p" || exit 0
+		r=${REASON[$p]:-unknown}
+		if ((major == 5)); then
+			case $r in
+			user) r=User ;;
+			dependency) r=Dependency ;;
+			weak-dependency) r='Weak Dependency' ;;
+			group) r=Group ;;
+			unknown) r='External User' ;;
+			esac
+		fi
+		[[ ${FAKE_DNF_REASON:-} != "$p="* ]] || r=${FAKE_DNF_REASON#*=}
+		printf '%s\n' "$r"
+		((major == 5)) || echo
+		;;
 	*' --upgrades '*) case $p in su-dummy-[abc]) printf 'skeptical-updater dummy %s (v2.0)\n' "$p"; ((major == 5)) || echo ;; esac ;;
 	*) case $p in su-dummy-new) printf 'skeptical-updater dummy su-dummy-new (v1.0)\n' ;; esac ;;
 	esac