Task: Improve Market Simulator status icons: clearer running/stopped and an auto_start=false indicator

The Market Simulator tree currently conveys feed running/stopped state via blue and yellow icons that are not visually distinct enough at a glance – surfaced during manual QA of the merged-theme Start-at-Root flow (see QA Market Simulator tree Start/Stop-at-Root for merged theme datasets), where 2026 Realistic's PLN-POLONIA curve looked, in the tree, like it had not started, even though backend logs confirmed it started cleanly and was publishing curve ticks throughout.

Separately, there is no visual indicator at all for auto_start = false feeds (e.g. Uniform Volatility Demo's IR curves, which deliberately don't bulk-start with their theme because they share (currency_code, index_name) pairs with 2026 Realistic and would trip curve_feed_controller's tenor-collision check). A tester watching a theme start has no way to tell, from the tree alone, why one of its feeds didn't come up alongside the rest.

Design and implement clearer status iconography covering both: an unambiguous running/stopped state, and a distinct marker for auto_start=false feeds.

• A feed's running vs. stopped state is distinguishable at a glance in the Market Simulator tree, without relying on colour alone (colour-blind-safe: shape/icon difference, not just hue).
• A feed with auto_start = false carries a distinct marker in the tree, visible whether or not its theme is currently running.
• Regression check: re-run the "Synthetic data themes" test scenario (Test Scenario: Synthetic data themes (2016 ORE Samples / 2026 Realistic / Uniform Volatility Demo) and the Start-at-Root theme picker) and confirm every started feed's status is unambiguous from the tree alone, with no need to cross-check service logs.

(Implementation strategy. Written when work starts; key decisions are distilled into the parent story's * Decisions at close, but the plan itself stays — it is the historical record of what we did.)

Manual QA scenarios (scaffolded via compass add test_scenario, run through the QA Validation Runner panel) that verify this task. Link new ones here as they're created; the scenario doc itself links back via its "Verifies task" field.