feat: playable arcade — rooms, identity, client, deployment

Round length is now bounded: the multiplier follows a hyperbolic curve
diverging at 60s, replacing an exponential one where a 275x crash point
produced a two-and-a-half minute round.

Fixes seed reveal, which silently failed every round because pgx cannot
encode a fixed-size byte array as bytea.

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

README.md

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+# Quantum Arcade
+
+A private physics arcade for one Linux box and the people on your network.
+Drop-in crash rounds, instant scratch tickets, a real double-entry ledger, and
+outcomes any player can verify on their own phone.
+
+## What it is
+
+Three shared crash games — a rocket fighting gravity, a decaying orbit, and a
+stacking tower — running on a five-minute heartbeat, plus instant scratch
+tickets to play between rounds. Identity is a keypair your browser generates;
+there is no account, no email, and no password.
+
+Everything runs on one machine: one Go binary with the client embedded,
+PostgreSQL, and Redis.
+
+## Running it
+
+```bash
+docker compose up -d
+```
+
+Then open `http://<your-box>:8080` from any phone on the network.
+
+To play with test funds before Lightning is wired up:
+
+```bash
+ARCADE_DEV_FAUCET=1 docker compose up -d
+```
+
+The faucet mints through the same ledger path a real deposit uses, so the code
+under test is the production code. Leave it off otherwise.
+
+## Development
+
+```bash
+docker compose up -d postgres
+go test ./...
+go run ./cmd/arcade
+```
+
+End-to-end tests need a live server:
+
+```bash
+ARCADE_DEV_FAUCET=1 go run ./cmd/arcade &
+ARCADE_E2E=http://localhost:8080 go test ./cmd/arcade/ -v
+```
+
+## How fairness works
+
+Before betting opens, the server generates a random seed and publishes
+`SHA-256(seed)`. It is now committed and cannot change its mind.
+
+The client seed is built from the public keys of everyone who joined the round.
+The operator does not choose who plays, so it cannot steer the outcome even
+knowing its own seed.
+
+The crash point is `HMAC-SHA256(serverSeed, clientSeed || nonce)`, run through
+the simulation. After settlement the seed is published, and the Verify tab
+recomputes the whole chain in your browser — it asks the server only for the
+published values, never for a verdict.
+
+Scratch tickets use the identical pipeline, and their odds tables are generated
+from the same data structure that produces outcomes, so the published odds
+cannot drift from reality. A test asserts observed frequencies and empirical
+return against the published figures across two million plays.
+
+## Architecture
+
+One binary, with enforced internal boundaries:
+
+| Package | Responsibility |
+|---|---|
+| `pkg/fixed` | Q32.32 fixed-point arithmetic; no floats, so results are identical everywhere |
+| `pkg/sim` | Deterministic RNG and the crash curve |
+| `pkg/fair` | Commit-reveal protocol and verification proofs |
+| `pkg/ledger` | Append-only double-entry accounting |
+| `pkg/scratch` | Scratch tickets and their published odds |
+| `pkg/identity` | Keypair sign-in via signed challenge |
+| `pkg/room` | Round lifecycle and live broadcast |
+
+Nine services on one machine would buy latency and 3am debugging, so this is
+one process. Modules talk through interfaces only; extracting one into its own
+service later is a transport change, not a rewrite.
+
+### Ledger invariants
+
+Enforced in the application and again by database constraints and triggers:
+
+- every transaction's postings sum to exactly zero
+- no account may go negative, except the Lightning bridge, whose negative
+  balance is by definition what is owed to players
+- rows are never updated or deleted; corrections are compensating entries
+
+`GET /api/health` sums every account. It must return zero. Anything else means
+the books are corrupt.
+
+### Round timing
+
+The multiplier follows `m(t) = 1/(1 - t/T)²`, which diverges at exactly 60
+seconds. No round can run longer, however extreme the crash point, and the
+climb visibly accelerates as it goes — which is where the tension comes from.
+
+## Status
+
+Built and tested:
+
+- fixed-point deterministic core, ledger, commit-reveal fairness
+- three crash games with live multiplayer rounds
+- two scratch tickets with verified-honest odds
+- keypair identity, peer-to-peer transfers, transaction history
+- in-browser verifier
+
+Not yet built:
+
+- **Lightning deposits and withdrawals.** The bridge account and ledger paths
+  exist; the node integration does not. The dev faucet stands in for now.
+- Tournaments and scheduled events
+- Operator dashboard
+
+## Scope
+
+This is built to run on a private network among people who know each other.
+It is not hardened for, and should not be exposed to, the public internet.
+Doing so would make it a public real-money gambling service, which carries
+licensing, KYC, and AML obligations this codebase does not address.