Keep clicking a notification working after a shell restart (#6636)

* Keep clicking a notification working after a shell restart

Notification actions lived only in the sending process: `-a` appended
`-A default=default`, so notify-send blocked on a D-Bus ActionInvoked signal and
the caller ran the command when it arrived. Nothing about that reached disk, so a
restored popup had no action to run and its sender stayed blocked forever.

Replace `-a` with `--exec <command>`, carried as an `omarchy-exec` hint into the
snapshot's `exec` role. It travels through the popup files and history, and the
shell runs it on click, so restored toasts behave exactly like live ones and the
sender exits immediately.

That drops the scaffolding whose only job was keeping a blocked sender alive: the
first-run invitations lose their `--show` re-entry and two transient units each,
omarchy-migrate-notify loses its transient service, and the screenshot,
recording, download, and taildrop toasts lose their wrapper subshells.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

* Keep a failed toast from failing the work it announces

Moving these sends out of their backgrounded subshells put a fallible command
on the foreground path, where the `&` used to swallow its exit status. A
notification outage — including the shell restart this branch targets — now
propagates:

- taildrop's receiver dies under `set -e` mid-delivery
- omarchy-capture-screenshot reports failure for a screenshot it already saved
- a completed download exits before scheduling its thumbnail cleanup, leaking
  the mktemp file

Announcing is best-effort in all three: the work is already done by the time
the toast goes out.

Also drop the first-run sleep that spaced out the welcome and Wi-Fi toasts.
It compensated for the background notify-send processes this branch removes;
each send now returns only once the server has taken the toast, so sending in
order is enough to stack them newest-on-top.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

* Stop tying the preview cleanup to the toast's expiry

The shell loads a notification thumbnail into memory when the toast appears and
never re-reads the file, so the preview only has to outlive that load. Deriving
the cleanup delay from the expiry was false precision, and it turned -t into a
variable for no reason: -t is already the helper's expiry setting.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>

test/shell.d/tailscale-receive-test.sh

@@ -25,14 +25,6 @@ SH
 cat >"$WORKDIR/bin/omarchy-notification-send" <<SH
 #!/bin/bash
 printf '%s\n' "\$*" >>"$WORKDIR/notifications"
-# Only the photo notification gets clicked.
-[[ \$* == *photo.png* ]] && echo default
-exit 0
-SH
-
-cat >"$WORKDIR/bin/xdg-open" <<SH
-#!/bin/bash
-printf '%s\n' "\$1" >>"$WORKDIR/opened"
 SH
 
 chmod +x "$WORKDIR/bin/"*
@@ -68,9 +60,14 @@ grep -q "^Received notes with space.pdf .* -g " <<<"$notifications" ||
   fail "taildrop receive announces other files with a glyph" "$notifications"
 pass "taildrop receive announces other files with a glyph"
 
-grep -qxF "$downloads/photo.png" "$WORKDIR/opened" ||
-  fail "taildrop receive opens a clicked file" "$(cat "$WORKDIR/opened" 2>/dev/null)"
-pass "taildrop receive opens a clicked file"
+# The shell keeps the click command with the toast, so receiving does not have
+# to sit blocked on an answer -- and the toast still opens the file after a shell
+# restart. Names with spaces have to arrive quoted for the shell to run them.
+grep -qF -- "--exec xdg-open $downloads/photo.png" <<<"$notifications" ||
+  fail "taildrop receive attaches the open command to the notification" "$notifications"
+grep -qF -- "--exec xdg-open $(printf %q "$downloads/notes with space.pdf")" <<<"$notifications" ||
+  fail "taildrop receive quotes spaced names in the open command" "$notifications"
+pass "taildrop receive lets a click open the received file"
 
 grep -q "unrelated.txt" <<<"$notifications" &&
   fail "taildrop receive leaves the rest of the downloads directory alone" "$notifications"