feat(adr-001): streaming event iterator over SubLinear orchestrator

[ruvnet]

Summary

The single-event call pattern (auto-tuned contrastive orchestrator + coherence gate + `PlanBudget`) was complete after PR #40. Real callers — RuView agents, Cognitum reflex loops — process an iterator of events, not a single one. This PR lifts the single-event call into a stdlib `Iterator` adapter.

API

```rust
pub fn event_stream_iter(
matrix: &dyn Matrix,
prev_solution: &[Precision],
events: I,
config: &EventStreamConfig,
budget: Option<&mut PlanBudget>,
) -> impl Iterator<Item = ProcessedEvent>
where I: Iterator<Item = (SparseDelta, Vec)>;

pub struct ProcessedEvent {
pub event_idx: usize,
pub anomalies: Vec,
pub latency: Duration,
pub status: EventStatus,
}

pub enum EventStatus { Solved, Skipped, BudgetRefused, Errored }
```

Pipeline per event

1. `delta_below_solve_threshold` skip gate (if cached coherence/min_diag supplied) → `Skipped` status.
2. `PlanBudget::try_consume` (if supplied) → `BudgetRefused` ends the iterator.
3. `contrastive_solve_on_change_sublinear_auto` for top-k anomalies → `Solved`.

Composition

```rust
for event in event_stream_iter(matrix, prev, events, &cfg, Some(&mut budget)) {
match event.status {
EventStatus::Skipped => continue,
EventStatus::BudgetRefused => break,
EventStatus::Solved => process(event.anomalies),
EventStatus::Errored => log_and_continue(),
}
}
```

Native composition with `.filter()`, `.take()`, `.collect()`, etc.

Test plan

• 5 `stream::tests::*` covering empty input, one-event-per-input with `Solved` status, skip-gate short-circuit on tiny delta, budget-exhausted termination, op-class compile-time
• `cargo test --lib -- stream::` → 5/5 pass
• `.github/complexity-baseline.txt` regenerated with `EventStreamOp` (SubLinear)
• Full CI

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