fix(swarm): deliver leader messages to in-process teammates

[glitch-ux]

Issue: #336

Problem

For teammates on the in-process backend, messages the leader sends never reach
the teammate — the write and read sides key the mailbox directory differently.

Mailboxes live at ~/.openharness/teams/<team>/agents/<agent_id>/inbox/.

• InProcessBackend.send_message(agent_id="name@team", ...) writes to the inbox
  keyed by the bare agent name — agents/<name>/inbox/
  (src/openharness/swarm/in_process.py:525). This is the convention used
  everywhere else in the swarm (write_to_mailbox(recipient_name, ...),
  permission_sync's worker_id / leader_id="leader", and the "leader"
  idle-notification target at in_process.py:284), and it is pinned by the
  existing test_send_message_writes_to_mailbox.
• start_in_process_teammate polls the inbox keyed by the fully-qualified
  name@team id — agents/<name@team>/inbox/
  (src/openharness/swarm/in_process.py:245).

agents/<name>/inbox/ ≠ agents/<name@team>/inbox/, so the teammate polls a
directory the leader never writes to. Both user_message and mailbox-based
shutdown deliveries are silently dropped.

Change

• Poll the inbox keyed by config.name (the bare agent name) so the read side
  matches the write side and the rest of the swarm.
• Add test_teammate_receives_message_sent_by_leader, which drives one real
  teammate query turn (stubbing run_query to yield a single event) and
  asserts the leader's message is drained and marked read from the inbox. It
  fails on main (message stays read=False) and passes with this change.

One-line runtime change; no public API change.

Verification

uv run pytest tests/test_swarm/ -q      # 138 passed (137 before + the new test)
uv run pytest -q                        # only the 2 pre-existing, unrelated
                                        # skill-registry failures remain

The new test fails without the fix and passes with it.