Phase 15: snapshots, forks, export/import, cognitive replay, experiments

- snapshots: checksummed JSON archive of every mind-scoped state table plus
  identity/personality/config and the event position; stored, downloadable
- fork: restore into a new mind with all ids remapped; event references are
  kept so history before the fork is shared by reference
- export/import: same archive; import is hostile-input validated (size,
  allow-listed tables, row caps, column names, checksum, forced mind_id)
- compare: deterministic counts, belief diffs by proposition, personality
  and config diffs, event mix
- replay: Runtime.Step for synchronous drivers; sandbox fork driven one
  stimulus at a time under a forbidden capability context; recorded model
  responses via a replaying router; steps labelled exact / approximate /
  diverged with recorded-vs-replayed digests
- experiments: definition (overrides, stimuli, expectations, seed, duration),
  background run in a disabled subject mind, stored and exportable results
- migration 0015, API, UI (Snapshots and Replay tabs, Experiments section,
  compare page), noemactl snapshots/compare/replay/experiments, docs

web/static/app.css

@@ -227,3 +227,6 @@ canvas.graph { width: 100%; height: 560px; display: block; border-radius: 8px; b
 
 /* Integrations */
 .badge.is-ok { background: var(--ok-soft); color: var(--ok); } .badge.is-stale { background: var(--warn-soft); color: var(--warn); } .badge.is-error { background: var(--danger-soft); color: var(--danger); } .badge.is-new, .badge.is-disabled { background: var(--surface-2); color: var(--muted); }
+
+/* Study: replay & experiments */
+.replay-step { padding: .6rem 0; border-top: 1px solid var(--border); } .replay-step:first-child { border-top: 0; } .replay-step ul { margin: .2rem 0 0 1rem; padding: 0; } .strong { font-weight: 600; }