docs: brokers are consumer nodes (C10), several attachable for comparable curves

Correct the broker mechanism: a broker is an ordinary downstream consumer node (C8/C9), not an external plugin/subsystem. It consumes the position-event stream + price streams and emits an equity stream; several brokers (e.g. sim-optimal pip + realistic currency) can be attached to the same position table at once, yielding directly comparable equity curves. Updates C10, CLAUDE.md invariant 7, aura-engine/aura-std crate docs, and the day-in-the-life doc.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

CLAUDE.md

@@ -76,11 +76,13 @@ design decision, not a refactor, and belongs in the ledger.
    outputs not an equity curve but a time-ordered table of position events
    (`event_ts, action[buy/sell/close], position_id, instrument_id, volume`; a
    position's open time is its opening event's `event_ts`); the set of open
-   positions at t is its state. Brokers are downstream, swappable plugins that
-   turn this table into an equity curve — never part of the strategy. Neutral
-   evaluation uses a deterministic, frictionless sim-optimal broker producing
-   synthetic equity in **pips**; realistic broker plugins add real
-   friction/constraints in currency for viability and deploy.
+   positions at t is its state. Brokers are downstream **consumer nodes** (not part
+   of the strategy) that consume the position-event stream (plus prices) and emit
+   an equity stream; several can be attached to the same position table at once,
+   giving directly comparable curves. Neutral evaluation uses a deterministic,
+   frictionless sim-optimal broker producing synthetic equity in **pips**;
+   realistic broker nodes add real friction/constraints in currency for viability
+   and deploy.
 8. **Deploy artifacts are frozen.** Hot-reload (cdylib) is an authoring-loop
    tool only. The live bot is a statically-linked, versioned, frozen artifact —
    never hot-swapped (audit trail: this bot = this commit).