P5 exit: usage metering, credit billing, promo codes, 3-step wizard

- LlmEvent::Usage across all three providers (Scripted deterministic
  word-count accounting; Anthropic message_start/delta usage; OpenAI-compat
  stream_options include_usage)
- tc-billing: ceil(tokens/1000) min 1 credit; lots drain oldest-first under
  FOR UPDATE; balance clamps at zero while the usage ledger records the
  full obligation; promo codes redeem exactly once via CAS (migration 0006)
- Runtime charges every completed run (billing failure never fails a run);
  proven: 1 token in + 3 out -> 1 credit deducted
- API: GET /api/team/usage, POST /api/credits/redeem (409 on reuse, audited)
- Credits page: balance, 7-day usage meter with runway estimate, PromoRedeem
- /claws/new is the full §9 wizard: ?step=identity|access|slack deep-linked
  progress, accent swatches + name randomizer, access toggles, optional
  Slack step, explicit review-and-confirm (creation = live agent), animated
  provisioning state -> straight into chat
- E2E: chat decrements the visible balance and fills the usage meter;
  WELCOME500 adds exactly 500 once then refuses; wizard round trip

140 Rust + 63 frontend tests + 23 Playwright journeys.

Co-Authored-By: Claude Fable 5 <[email protected]>

.cargo/config.toml

@@ -0,0 +1,12 @@
+# Point the whole test suite at the persistent shared Postgres managed by
+# `scripts/test-server.sh up`. With TC_TEST_DATABASE_URL set, tc-testkit never
+# starts a per-test `postgres` testcontainer (it takes its `_container: None`
+# branch), so a killed/panicking/orphaned `cargo test` has nothing to leak.
+# This is the durable fix for the runaway `postgres:11-alpine` containers.
+#
+# Not forced: an explicit TC_TEST_DATABASE_URL in the environment still wins
+# (e.g. CI pointing at its own server). If the shared server is down, tests
+# fail fast with a connection error instead of silently leaking containers —
+# run `scripts/test-server.sh up` first.
+[env]
+TC_TEST_DATABASE_URL = "postgres://postgres:[email protected]:54331/postgres"