W06.A.3: wire LD_PRELOAD shim notifications into journal events

[espadonne]

Summary

Daemon's shim_listener::handle_one previously acked Allow and
discarded the ShimNotification. W06.A.3 wires it through:

1. Resolve pid → CommandId via ActiveCommands::resolve_by_descendant.
2. Classify the syscall → TreeOp::Unlink (unlink/unlinkat) or
   TreeOp::Rename (rename/renameat).
3. Journal via Index::put_event.
4. Then ack Allow (resolution happens BEFORE ack to avoid the
   ps -p race against fast-dying emitter pids — see comment).

Headline result

make-install-undo-fbsd.sh transitions from documenting-the-gap
(applied=0, files remain) to Outcome A: full undo:

[smoke] shim notifications observed by daemon: 2
[smoke] journal events: 2
[smoke] OUTCOME A — full undo (install-target reverted, source unchanged)
[smoke] PASS: make-install-undo-fbsd (Outcome A)

/usr/bin/install's two rename(temp→final) calls fire the shim
interposer (W06.A.2's versioned exports), notifications reach the
daemon (W06.A.2's .symver plumbing), the daemon resolves each
pid back to the smoke's command, journals two TreeOp::Rename
events, and shit undo --yes emits the inverse renames + cleans
the install-target.

Race fix

Initial impl resolved pid → CommandId AFTER acking the shim;
the emitter (e.g. install) terminates within ~10ms of the ack,
and our ps -p <pid> resolution returns empty. Notifications
arrive in the daemon but the journal stays empty.

Fix: resolve synchronously BEFORE ack. Costs ~10ms per
notification (one ps -p per ancestor level) but fits inside
the shim's 50ms allow-on-timeout budget. Followup
W06.A.4-or-later carries ancestry inline in the wire to
eliminate the shell-out entirely.

Out of scope (W06.A.4)

• Pre-image capture for open/truncate/pwrite/mmap —
  these modify content, need pre-mutation bytes via SCM_RIGHTS.
  Currently dropped with a debug log.
• Ancestry-in-wire (eliminate the ps -p cost).
• W08's mv smoke gates — needs the smoke to set LD_PRELOAD for
  mv itself. Documented in .docs/sprints/W/W06.A/followups.md.

Test plan

• cargo test -p shitd — 127 tests pass (incl
  shim_listener::one_shot_notify_round_trip).
• cargo fmt --check, cargo clippy -p shitd --all-targets -- -D warnings clean.
• All 8 W smokes on shit-fbsd PASS, including
  make-install-undo-fbsd now at Outcome A.
• freebsd-smoke (B04) CI green.