add autonomous exploration loop
phi can now research people and topics in the background. when a new
handle interacts with phi, an explore_handle item gets queued on phi's
PDS. on a schedule (default 16:00 and 20:00 UTC), phi claims one item,
runs a research pass with its MCP tools, and writes findings either to
the user's namespace as exploration_note (lowest trust tier) or to
episodic memory.
queue lifecycle is explicit: pending -> in_progress -> completed | failed.
crashes mark items as failed instead of silently dropping them. dedup
blocks both pending and in_progress items by kind+subject.
self-reinforcing loops are guarded: _maybe_enqueue_exploration counts
both observations and exploration_notes toward the threshold, so once
phi has explored someone it won't re-enqueue them on every interaction.
trust tier docs updated with tier 5 (background research, lowest trust).