Close the plan: screenshots and a measured performance pass

- docs/screenshots: nineteen pages captured with headless Chromium from a
  running instance; README gains a screenshot section
- tests/perf: opt-in load test (NOEMA_PERF=1) seeding 60k events, 6k
  memories and 1.5k beliefs across two minds, timing sixteen hot reads
  against a 400 ms ceiling and rejecting sequential-scan plans
- migration 0016: indexes the test found missing (memories by mind and
  recency, beliefs by mind and confidence, events by mind and category,
  belief versions by mind and time)
- docs/performance.md records the numbers and how to rerun

docs/performance.md

@@ -0,0 +1,50 @@
+# Performance pass
+
+`tests/perf` is an opt-in load test. It seeds a fresh schema with a realistic
+volume for one mind plus a second "noise" mind (so scoping matters), times
+the hot read paths in steady state, and rejects any plan that sequentially
+scans the three large tables.
+
+```
+NOEMA_PERF=1 NOEMA_TEST_DATABASE_URL=postgres://... go test -count=1 -v -run TestHotPaths ./tests/perf/
+```
+
+Seed: 60 000 events, 6 000 memories, 1 500 beliefs with evidence. Ceiling per
+read: 400 ms (a regression guard, not a target).
+
+## Results (PostgreSQL 16 in Docker, laptop, 2026-09-14)
+
+| Read | Before 0016 | After 0016 |
+|---|---|---|
+| events recent 50 | 3.2 ms | 1.2 ms |
+| events by type | 1.8 ms | 1.1 ms |
+| events after seq (runtime cursor) | 2.2 ms | 1.2 ms |
+| events summary search | 3.3 ms | 1.4 ms |
+| events stats (group by category) | 13.8 ms | 15.8 ms |
+| memory list 50 | 4.1 ms (seq scan) | 0.5 ms |
+| memory text search | 1.7 ms | 0.5 ms |
+| memory fused retrieve | 31 ms | 27 ms |
+| beliefs list | 3.6 ms (seq scan) | 3.6 ms |
+| beliefs search / contested / uncertain / stats / recent changes | ≤ 3 ms | ≤ 3 ms |
+| snapshot capture (all state tables) | 288 ms | 296 ms |
+
+Migration `0016_hot_path_indexes` adds the indexes the planner needed for the
+two list orders that had fallen back to sequential scans, plus
+`(mind_id, category, seq)` on events for replay's stimulus scan and
+`(mind_id, created_at)` on belief versions for the recent-changes view.
+
+## What was deliberately left alone
+
+- **Fused retrieval (~27 ms)** is the most expensive per-cycle read; it runs a
+  ranked full-text query capped at 50 candidates plus optional vector search.
+  It is well inside the cycle budget; tune only if cycle latency becomes visible.
+- **Snapshot capture (~300 ms)** serialises every state table; it is an
+  operator action, not a cycle path.
+- **Event stats (~16 ms)** is a group-by over all of a mind's events, used on
+  the overview page. A materialised counter would be premature at this volume.
+
+## Rerun before touching queries
+
+The plan checks fail loudly when a future query drifts off its index, which is
+the cheapest way to catch a regression that would otherwise only show up with
+months of history.