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]>

.sqlx/query-47c1cee8591250819d22e87058c6011bebb77eaf93c1cfa2535db42221d8ecf3.json

@@ -0,0 +1,34 @@
+{
+  "db_name": "PostgreSQL",
+  "query": "SELECT tokens_in, tokens_out, credits FROM usage_events\n               WHERE workspace_id = $1",
+  "describe": {
+    "columns": [
+      {
+        "ordinal": 0,
+        "name": "tokens_in",
+        "type_info": "Int8"
+      },
+      {
+        "ordinal": 1,
+        "name": "tokens_out",
+        "type_info": "Int8"
+      },
+      {
+        "ordinal": 2,
+        "name": "credits",
+        "type_info": "Numeric"
+      }
+    ],
+    "parameters": {
+      "Left": [
+        "Uuid"
+      ]
+    },
+    "nullable": [
+      false,
+      false,
+      false
+    ]
+  },
+  "hash": "47c1cee8591250819d22e87058c6011bebb77eaf93c1cfa2535db42221d8ecf3"
+}