0.2.39: bitcoin-denominated view, first-login flow, unfunded + tax center

- BTC prices: btc_prices table, CSV upload on Import page (auto-detected
  date/close columns, upsert by date), entities.close_date as the BTC entry
  mark; statements carry btc_price_cents (as-of) + btc_close_price_cents.
  LP capital blocks show paid-in vs current value in bitcoin terms.
- First login: accounts on the shared default password are flagged
  (must_change_password) and blocked behind a full-screen password change;
  external accounts then get a one-time welcome tour with a 2FA offer
  (users.onboarded_at).
- LP portal: Unfunded (callable commitment) metric; Tax documents center
  aggregating K-1/tax docs across funds, grouped by year.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

backend/ten31portal/routers/entity_router.py

@@ -294,7 +294,9 @@ def update_entity(
         setattr(entity, key, val)
     session.add(entity)
     session.flush()
-    record_audit(session, user.id, "update", "entity", entity.id, changes)
+    # mode="json" so date fields (close_date) serialize into the audit JSON column.
+    record_audit(session, user.id, "update", "entity", entity.id,
+                 body.model_dump(exclude_unset=True, mode="json"))
     session.commit()
     session.refresh(entity)
     return EntityResponse.model_validate(entity, from_attributes=True)