feat(telemetry): record per-agent usage for mission turns

The command centre's SPEND, ACTIVITY and THROUGHPUT cards read `usage_events`,
and nothing on the mission path ever wrote a row: `cm_billing::charge` was
called only from the agent-run path. Measured mid-mission with 14 agents live,
`usage_events` was 0 while a crew had just burned 15k tokens — so an agent that
had done real work reported zero cost and zero activity.

The worker already knew everything needed: it logs node, role and token count
per step, and the node's `attrs.agent` carries the `claw_<uuid>` binding the
runtime dispatches on. This routes that to the ledger.

`charge`'s run_id is now Option. `usage_events.run_id` references `agent_runs`,
and a topology turn has no row there — passing its `topology_runs` id was a
foreign-key violation, which is exactly what the first attempt hit. NULL is the
honest value; the agent-run caller still passes its real id.

The executor reports one total rather than an in/out split, so the cost is right
(credits price the sum) and the columns record it as output rather than
inventing a split.

Verified end to end on a real mission: 4 agents, 1046-8670 tokens each, credits
attributed per agent, and the SPEND/ACTIVITY queries now return real numbers.

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

crates/cm-billing/src/lib.rs

@@ -29,7 +29,11 @@ pub async fn charge(
     pool: &PgPool,
     workspace_id: WorkspaceId,
     agent_id: AgentId,
-    run_id: Uuid,
+    // Optional: `usage_events.run_id` references `agent_runs`, and a topology
+    // turn has no row there — its id lives in `topology_runs`. Passing that id
+    // was a foreign-key violation, so mission usage went unrecorded. NULL is
+    // the honest value for a charge that is not an agent_run.
+    run_id: Option<Uuid>,
     input_tokens: u64,
     output_tokens: u64,
 ) -> Result<i64, BillingError> {