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/data/zypper/info-su-dummy-orphan-parent.txt

@@ -0,0 +1,19 @@
+
+
+Information for package su-dummy-orphan-parent:
+-----------------------------------------------
+Repository     : su-dummy
+Name           : su-dummy-orphan-parent
+Version        : 1.0-1
+Arch           : noarch
+Vendor         :
+Installed Size : 27 B
+Installed      : No
+Status         : not installed
+Source package : su-dummy-orphan-parent-1.0-1.src
+Summary        : skeptical-updater dummy su-dummy-orphan-parent (v1.0)
+Description    :
+    Dummy package su-dummy-orphan-parent version 1.0 for skeptical-updater tests.
+
+    Second paragraph of su-dummy-orphan-parent 1.0 (blank line above on purpose).
+