fix(show): star marker, aligned gutter and smarter AUR merge

N?? / show marks the upstream candidate with "*" instead of ">" (the
prompt, which read as a command in logs), and every line but the note
gets a two-character gutter: "  " for the installed record, "* " for the
candidate, so keys and colons line up. The plain native fallback (zypper,
unmergeable records) and the not-installed candidate use the same gutter.

pacman records (-Qi with -Si or the AUR helper's -Sia) are now compared
the way they are meant:
- values unwrapped (continuation lines joined, runs of blanks as one):
  yay wraps Depends On / Optional Deps at 80 columns even without a
  terminal unless COLUMNS=0, which the helper now gets for -Qua and -Sia
- Depends On, Provides, Conflicts With, Make/Check Deps and the other
  lists as sets of exact tokens in any order (a constraint is a change)
- Optional Deps by package names ("name: description [installed]" in
  -Qi, bare names from the AUR)
- a differing value is one line like -Qi, Optional Deps one entry per
  line; candidate-only fields sit next to their counterpart (Repository
  after Version, AUR URL after URL, Maintainer after Packager, ...)

Verified on recorded claude-desktop records (paru 2.1.0, yay 13.0.1, the
installed 2.9939.4-1 from the AUR's own .SRCINFO); discovery/pacman.md
section 15.2.

tests/unit/interactive.bats

@@ -93,11 +93,10 @@ UPGRADE='apt-get -y -o Dpkg::Options::=--force-confdef -o Dpkg::Options::=--forc
 @test "N?? prints the installed record merged with the candidate" {
 	run skup --no-refresh <<<$'1??\nq'
 	assert_success
-	assert_line '# lines starting with > come from the upstream candidate: a differing value, or a field the installed record lacks'
-	assert_line 'Package: su-dummy-a'
-	assert_line 'Version: 1.0'
-	assert_line '> Version: 2.0'
-	assert_line '> Depends: su-dummy-b (>= 2.0)'
+	assert_line '# lines starting with * come from the upstream candidate: a differing value, or a field the installed record lacks'
+	assert_line '  Package: su-dummy-a'
+	assert_output --partial "$(printf '%s\n' '  Version: 1.0' '* Version: 2.0')"
+	assert_line '* Depends: su-dummy-b (>= 2.0)'
 	log_has 'dpkg-query -s -- su-dummy-a'
 	log_has 'apt-cache show --no-all-versions su-dummy-a'
 }