fix(providers): promote weekly window to primary for Qwen Cloud

[hellhole8]

Summary

Fixes Qwen Cloud individual plans that expose only the weekly usage window
(per1WeekPercentage, no per5HourPercentage / legacy quota). Previously
snapshot_to_usage failed with "Qwen Cloud usage windows missing"; now the
weekly window is promoted to primary.

Behavior change

• Weekly-only accounts now show the weekly percentage (e.g. 84.39%) instead
  of no data / error.
• When both windows exist, weekly remains secondary (unchanged).
• Added test weekly_only_shape_promotes_weekly_to_primary with real-world
  fixture.

Commands run

• cargo test -p codexbar qwencloud — 9/9 pass
• cargo fmt --all

Validation

Validated in the desktop app (debug build): provider now shows the weekly
84.39% window correctly.

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[Finesssee]

Thanks for the PR, I will review it ASAP