feat(apollo-react): add IterationNavigatorPill component and Execution Count story

Extracts the Option B iteration navigator from the V2 story proposals into a
standalone reusable component. IterationNavigatorPill is a unified segmented
pill with an All aggregate toggle, per-iteration status dots, click-to-type
jump, and a crosshair shortcut to the first failed iteration. Adapts
responsively across three size tiers (full ≥400px, compact 260-399px,
minimal <260px) derived from props.width.

Adds LoopIterationPillState to LoopNode.types and exports the component
from the LoopNode module index. Adds an Execution Count doc-layout story
to Components/LoopNode showing all three tiers in a live canvas preview
with anatomy cards, breakpoint spec table, and usage code block.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: 1980computer