perf + simpler: composite index, range-filtered protokoll, simpler profile

- Migration v9 adds idx_applications_user_flat_started on
  (user_id, flat_id, started_at DESC). Covers latest_applications_by_flat
  inner GROUP BY and the outer JOIN without a table scan.
- Push the protokoll date range into SQL instead of pulling 5000 rows
  into Python and filtering there: new audit_in_range / errors_in_range
  helpers with a shared _range_filter_rows impl. Protokoll page limits
  500, CSV export 5000.
- _row_to_profile collapses to `dict(profile_row)`. ProfileModel (Pydantic)
  already validates and coerces types on the apply side, extras ignored.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

web/db.py

@@ -260,6 +260,11 @@ MIGRATIONS: list[str] = [
     CREATE INDEX IF NOT EXISTS idx_partnerships_from ON partnerships(from_user_id);
     CREATE INDEX IF NOT EXISTS idx_partnerships_to   ON partnerships(to_user_id);
     """,
+    # 0009: composite index for latest_applications_by_flat + last_application_for_flat
+    """
+    CREATE INDEX IF NOT EXISTS idx_applications_user_flat_started
+        ON applications(user_id, flat_id, started_at DESC);
+    """,
 ]
 
 
@@ -780,6 +785,36 @@ def recent_audit(user_id: Optional[int], limit: int = 100) -> list[sqlite3.Row]:
     ).fetchall())
 
 
+def _range_filter_rows(table: str, ts_col: str, start_iso: Optional[str],
+                       end_iso: Optional[str], limit: int) -> list[sqlite3.Row]:
+    """Date-range filtered fetch from an append-only table. Pushes the
+    timestamp filter into SQL so we don't drag 5000 rows into Python just
+    to discard most of them."""
+    clauses, params = [], []
+    if start_iso:
+        clauses.append(f"{ts_col} >= ?")
+        params.append(start_iso)
+    if end_iso:
+        clauses.append(f"{ts_col} < ?")
+        params.append(end_iso)
+    where = ("WHERE " + " AND ".join(clauses)) if clauses else ""
+    params.append(limit)
+    return list(_get_conn().execute(
+        f"SELECT * FROM {table} {where} ORDER BY {ts_col} DESC LIMIT ?",
+        params,
+    ).fetchall())
+
+
+def audit_in_range(start_iso: Optional[str], end_iso: Optional[str],
+                   limit: int = 500) -> list[sqlite3.Row]:
+    return _range_filter_rows("audit_log", "timestamp", start_iso, end_iso, limit)
+
+
+def errors_in_range(start_iso: Optional[str], end_iso: Optional[str],
+                    limit: int = 500) -> list[sqlite3.Row]:
+    return _range_filter_rows("errors", "timestamp", start_iso, end_iso, limit)
+
+
 # ---------------------------------------------------------------------------
 # Retention cleanup
 # ---------------------------------------------------------------------------