fix: close the four known installer bugs (DU-H1, DU-H2, BUG-1, BUG-2)

- DU-H1: flags are parsed wherever they sit, so `install --unattended`
  and `--unattended install` are the same run; any unknown flag, word,
  or subcommand exits 2 to stderr before a package manager is touched.
- DU-H2: every download lands in one private mktemp -d (mode 700)
  workdir per run, is checked non-empty before sudo tar sees it, and an
  EXIT/INT/TERM trap cleans up. No fixed /tmp paths remain.
- BUG-1: ^t is now toggle-shown — it ticks only the rows the active
  filter is showing, and @needs expansion stops at the first invasive
  row, so an invasive package can never be ticked off-screen.
- BUG-2: ^t journals what it added, so a second ^t over the same shown
  set unticks exactly that set; the bind no longer clears the query.
- lab: the type verb polls fzf's reported query to a deadline instead
  of a fixed sleep; marks_settled retries within its deadline.

Suite 256/0 host, 214/0 docker (ubuntu:24.04), mutations 24/24 killed
(six new mutants re-introduce each bug and all die), lab 6/6 green.

.tests/mutations/21-unknown-flag-ignored.mut

@@ -0,0 +1,9 @@
+# what: an unrecognised flag is skipped instead of stopping the run
+# why:  the other half of DU-H1 -- a parser that shrugs at `--unatended` installs a different set of packages than the operator asked for, with no way to tell
+# kills: an unknown flag after the subcommand is refused
+# run:  unit
+<<<OLD
+		-?*)          err "unknown flag: $a"; usage; exit 2 ;;
+<<<NEW
+		-?*)          continue ;;
+<<<END