feat(billing): agent-side spend records who was paid

Judge spend gained provider, model and mission on 2026-09-14; agent spend —
the larger half — did not. The runtime's `done` frame has always carried
`model` and `provider` beside the two token counts, and `topology_exec` read
only the counts, summed them, and charged the sum as output with no record of
which provider served the turn.

`TurnOutcome` and `StepRecord` carry a `Spend` now (input/output split,
provider, model), the worker passes it through `cm_billing::charge` along with
the mission id, and the chat runtime records the model it requested — that
loop drives one provider with no chain, so requested is answered. A bare
model name is recorded without a guessed family. `StepRecord.spend` is
`serde(default)` so journaled checkpoints from before this field still load,
and `tokens` stays as the total every reader keys on.

`charge` moved from `query!` to `query`: the macro pins the statement to
offline metadata that a schema change then has to regenerate against a live
database, for columns that are nullable text and uuid.

The done-frame test now asserts the split and the provider survive, not just
the sum.

Co-Authored-By: Claude Opus 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01WZb5A2kfVfjpdwSochkuHz

crates/cm-api/src/recursive_exec.rs

@@ -173,6 +173,7 @@ impl TurnExecutor for SubTopologyExecutor {
             output: record.final_output,
             tokens: record.totals.tokens,
             gated,
+            spend: Default::default(),
         })
     }
 }