Email search/query + windowed digest preview (v0.1.0:83)

Communications tab (search/query roadmap items 1 & 2):
- Fix the investor dropdown: the facet only listed grid investors, so it
  came back empty whenever email matched a classic contact or org domain
  (no grid id — the common case). It now mirrors the email list, resolving
  each link to a typed identity (fund:/org:/contact:/addr:) with precedence
  grid -> org -> contact -> address; investor_id accepts the typed key
  (bare id = fund: for back-compat) and an unknown prefix matches nothing.
- Add a date-range filter and a click-to-expand full-body view
  (GET /api/email/detail, admin, soft-delete-gated; body_text only, never
  raw remote HTML).
- Add a "Search content" mode: GET /api/email/search wraps the ingest
  hybrid_search over the Qdrant email index (doc_type=email), hydrated and
  soft-delete-filtered against SQLite (canonical), 503 if Spark/Qdrant down.

Daily digest:
- Settings -> Admin builds a digest over a chosen window (last 24h or since
  a date) as an in-app preview before sending (POST /api/admin/digest/preview),
  so the local-Spark summarizer can be verified on demand even on a quiet day.
  Manual send uses the same window; neither advances the daily cursor, so a
  preview never suppresses the scheduled digest.

Code-only, migrations no-op. 22/22 backend tests, render-smoke pass.

backend/email_integration/digest_scheduler.py

@@ -100,15 +100,36 @@ def _build_and_send(conn, since_iso, until_iso, *, build_fn=None, send_fn=None):
     }
 
 
+def send_digest_window(conn_factory=None, *, since_iso, until_iso,
+                       build_fn=None, send_fn=None):
+    """Build the digest for an explicit (since_iso, until_iso] window and send it
+    to the active-admin set now, WITHOUT advancing the daily cursor — a manual or
+    preview send must never suppress the scheduled daily digest. Same transport +
+    recipient rules as the daily path (raises digest_mailer.NoTransport when none
+    is configured / no admin has an address). Backs the admin 'send now' endpoint.
+
+    No DB writes happen here (the cursor is deliberately untouched), so the connection
+    is opened and closed without a commit — don't add one without revisiting that."""
+    factory = conn_factory or _conn_factory_from_env()
+    conn = factory()
+    try:
+        result = _build_and_send(conn, since_iso, until_iso,
+                                 build_fn=build_fn, send_fn=send_fn)
+        return {"status": "sent", **result}
+    finally:
+        conn.close()
+
+
 def maybe_send_digest(conn_factory=None, *, force=False,
                       now_local=None, now_utc=None, build_fn=None, send_fn=None):
     """Send the daily digest if it is due (or unconditionally when force=True).
 
-    Daily path: skips before the send hour and if already sent today; content
-    window runs from the last send to now and the cursor advances on success.
-    force path (the admin 'send now' endpoint): ignores the policy and the guards,
-    uses a fixed last-24h window, and does NOT advance the daily cursor — so an
-    on-demand preview never suppresses the scheduled send."""
+    Daily path (the scheduler loop): skips before the send hour and if already sent
+    today; content window runs from the last send to now and the cursor advances on
+    success. force path: ignores the policy and the guards, uses a fixed last-24h
+    window, and does NOT advance the daily cursor. (The admin 'send now' / preview
+    endpoints now use send_digest_window for an arbitrary window; force is retained
+    for the fixed last-24h case and its tests.)"""
     import digest_builder
 
     factory = conn_factory or _conn_factory_from_env()