Stable review indices and deduplicate tag taxonomy

Review items now get a stable scan_index assigned during scan, so
sequential review commands don't target wrong emails after earlier
items are resolved. Indices reset on each new scan.

Deduplicate tag taxonomy from 21 to 14 tags: drop invoice/payment
(covered by billing), delivery (covered by shipping), discount/marketing
(covered by promotion), and generic notification/update tags.

scripts/email_processor/classifier.py

@@ -28,11 +28,11 @@ import decision_store
 LOGS_DIR = Path(__file__).parent / "logs"
 
 TAG_TAXONOMY = [
-    "receipt", "invoice", "payment", "billing",
-    "shipping", "delivery",
-    "promotion", "discount", "marketing", "newsletter",
-    "notification", "security", "social",
-    "reminder", "confirmation", "update", "alert",
+    "receipt", "billing",
+    "shipping",
+    "promotion", "newsletter",
+    "security", "social",
+    "reminder", "confirmation", "alert",
     "personal", "account", "subscription", "travel",
 ]