Projects an account's cash forward over upcoming dates, starting from the
settled cash balance and applying every known future cash event in date
order. Answers "will cash be available on date X".

The timeline combines five kinds of event:

• Live holds — cash already reserved against the account (open orders,
  cash raises), dated today.
• Committed cash raises: raises that will be funded but are not
  reserved yet, including every instance a recurring schedule has
  generated, each dated on the day it will be activated. A raise moves
  from this kind to a live hold on that date without changing the
  projected total. Only present for organizations where committed
  cash-raise projection is enabled; contact Moment to have it enabled.
  Where it is off, a raise reaches the timeline only once it is
  activated, and every other kind of row is unaffected.
• Unsettled trades — each executed-but-unsettled trade appears
  twice: a pending_buy / pending_sell row on its trade date that
  lands in the unsettled bucket, and a buy / sell row on its
  settlement date that moves the same amount from unsettled into settled.
  The second row does not change running_total.
• Fixed-income cashflows — coupon and maturity rows for bonds held
  in the account.
• Dividends — dividend rows, for organizations where dividend
  projection is enabled. Contact Moment to have it enabled.

Each row carries the running unsettled and settled bucket balances
after that event is applied; running_total is always their sum and is the
projected total cash as of that row's date.

Projection window. Coupon, maturity, and dividend rows extend roughly
180 days forward, and a recurring cash raise's instances roughly 365 days
forward. A schedule running past that has occurrences it has not
generated yet, so they do not appear. Holds and unsettled trades are
always complete. Absence of a row beyond those windows does not mean no
event is due.

Best-effort cashflows. Coupon, maturity, and dividend rows come from an
upstream service. If that service is unavailable the endpoint still returns
200 with the holds and trade rows, and the cashflow rows are simply
absent — the response does not currently distinguish "no cashflows due"
from "cashflows could not be retrieved". Holds and unsettled trades are
always complete and are unaffected.

An account with no cash and no activity returns 200 with a zero
settled_cash and an empty projections list, not a 404.