Remove magic startup-step count from navigation test helper

[adrunkhuman]

Problem

bootstrapLeagueLoadedModel() advances startup commands with a fixed loop bound of 4.

That makes the helper sensitive to implementation details in the startup async chain.

Current behavior

• the helper steps one command manually, then drains at most four more commands
• if startup gains another async step, tests can start failing in confusing ways or silently stop asserting the full flow

Why it matters

This is test infrastructure for navigation behavior, so it should track the startup flow robustly without embedding a magic number.

Suggested direction

• drain commands until nil instead of stopping after a fixed number of iterations
• keep assertions focused on the final loaded state rather than the current number of async transitions

Acceptance hints

• the helper completes regardless of small startup-flow refactors
• the fixed iteration count disappears
• fixture navigation tests still verify the expected loaded league state