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]>

crates/tc-llm/src/openai_compat.rs

@@ -97,6 +97,7 @@ impl LlmProvider for OpenAiCompatProvider {
             "max_tokens": request.max_tokens,
             "messages": OpenAiCompatProvider::wire_messages(&request),
             "stream": true,
+            "stream_options": {"include_usage": true},
         });
         if !tools.is_empty() {
             body["tools"] = Value::Array(tools);
@@ -159,6 +160,12 @@ impl LlmProvider for OpenAiCompatProvider {
                 if let Some(reason) = choice["finish_reason"].as_str() {
                     finish = Some(stop_reason(reason));
                 }
+                if let Some(usage) = data["usage"].as_object() {
+                    yield LlmEvent::Usage {
+                        input_tokens: usage["prompt_tokens"].as_u64().unwrap_or(0) as u32,
+                        output_tokens: usage["completion_tokens"].as_u64().unwrap_or(0) as u32,
+                    };
+                }
             }
             for (id, name, args) in pending.drain(..) {
                 if name.is_empty() {