fix(server): honor disabled usage hub polling

[yashranaway]

What Changed

Skip periodic usage hub refreshes when the provider health-check interval is disabled. Startup, settings changes, and explicit refresh still fetch the current limits.

Why

An interval of zero still polls configured CLIProxyAPI usage hubs once per minute while the Limits view is active. The loop substitutes a one-minute sleep, then fetches anyway.

Testing

• UsageLimitSources.test.ts passes, 2/2.
• Deterministic TestClock cases cover enabled and disabled polling and explicit refresh.
• Server typecheck, targeted lint, and formatting pass.

Checklist

• One focused change
• Explained what changed and why
• Added regression coverage for the changed behavior
• No UI layout or animation changes

Model: GPT-6 Astra
Harness: T3 code

Note

Fix 'UsageLimitSources.make' to honor disabled polling for non-positive intervals

• UsageLimitSources.make now skips scheduled provider-status refreshes when the configured interval is zero or negative. It retains a 60-second sleep to avoid tight looping but skips the BackgroundPolicy check.
• The initial forked refresh and explicit refresh requests remain unchanged.
• Adds a test-only BackgroundPolicy fixture and parameterized tests to verify read counts for zero and one-minute refresh intervals.
• Behavioral Change: Setting the refresh interval to 0 or a negative value now disables scheduled polling instead of falling back to periodic refreshes.

^{Macroscope summarized 2c566bd.}

[macroscopeapp]

Approvability

Verdict: Approved at 2c566bd

Macroscope's review found this PR approvable — This is a narrowly scoped server bug fix that makes the existing disabled polling setting suppress only scheduled usage-hub refreshes, while preserving startup, settings-change, explicit refresh, and enabled polling behavior. Deterministic tests cover both disabled and enabled intervals.

^{You can add or adjust custom eligibility rules. Learn more.}