feat: add temporal Mol explorer

docs/DATASET_STRATEGY.md

@@ -138,3 +138,20 @@ V1 dataset strategy is complete when:
 - an area can request/cache a reference building layer;
 - detection outputs can be compared with that reference layer;
 - exports include source metadata.
+
+## Temporal snapshots and evolution
+
+- A historical observation is one persisted dataset snapshot. Existing
+  datasets are not overwritten and features are not hidden in job JSON.
+- Related observations share a stable `temporal_series_key`; `observed_at`
+  records when the source describes reality, while `imported_at` records
+  ingestion time.
+- The latest-state map uses the latest available observation but must not call
+  an old source edition current reality.
+- Evolution metrics use the same selection geometry, aggregation and units for
+  both snapshots.
+- Partial-sector population is an area-weighted estimate. GeoIntel must not
+  imply address-level distribution when only sector totals are available.
+- Historical cartographic classes can change meaning between editions. Source
+  classes and processing notes remain provenance, and object changes require
+  explicit stable source identity.