v0.2.0 — leave on any day

A position can now be closed before maturity, in full or in part, and the USDC
comes back in the same transaction. The exit is paid from a backstop pool the
protocol funds, not from other depositors. The visitor sees the price to leave
before signing, and the transaction refuses to pay less than that price by more
than 0.1%.

What the release covers (US2):

• the exit screen breaks the quote down before the signature: current value
  of the position, the management fee owed so far, a spread proportional to
  the weighted remaining duration, and the amount that will arrive
• a partial exit takes the same share of every rung, so the ladder keeps its
  proportions; the client quotes it with the same arithmetic the program
  runs, checked against one shared set of fixtures in Rust and TypeScript
• the signed transaction carries a payout floor. A quote that moved too far
  by the time it lands is refused (QuoteDrift), and a pool too small to pay
  refuses the exit whole (BackstopInsufficient) instead of filling part of it;
  the screen offers the largest share the pool can cover
• after the signature the screen shows what was received next to what was
  quoted
• every exit emits LadderExited with the rating and price each rung left at
• the backstop is funded by the vault admin and cannot be withdrawn below
  the principal of open positions
• a landing page at the site root explains the deposit, the statement and
  the exit, and lists what the demo does not do; the app moved to /app/ and
  old links redirect

Also in this release:

• the deposit now waits for the network to confirm it. Before, "Position
  opened" appeared as soon as the wallet sent the transaction, the wallet
  balance on screen stayed stale, and a deposit sent right after a fresh
  custody setup could fail in simulation. Both transactions are now
  confirmed before the screen moves on, and the balance is read back from
  the chain.
• the repository carries the Apache-2.0 license text it already declared.

Measured on devnet over the public endpoint the deployed site uses, 100 exits
of different sizes (25 deposits, each left in 10%, 25%, 50% and 100% steps,
with a 20-second pause between quote and signature):

SC-003 signature to USDC in the wallet 4.07 s worst, 1.22 s median, of 10 s
SC-006 largest quote-to-payout gap 8 micro-USDC on a 222.50 quote
(0.036 ppm) of 0.1%, 0 refused

What this release does not do, and it matters:

• the ladder does not roll. Nothing reinvests a matured rung, so after the
  first maturity it stops being a ladder.
• nothing reacts to a downgrade, and the maintenance keeper is not running.
• the backstop pool on devnet is finite and demo-funded. Large exits can be
  refused until it is topped up.
• the ratings and the issuers are ours. There is no Moody's or AlphaLedger
  feed, the instruments are minted by our own demo issuer, and the route is
  deterministic — so a quote matching its payout proves the arithmetic, not
  behaviour on a real market.
• no audit, and no regulatory compliance of any kind.

Not real securities, ratings, or offers.