fix: prevent animation loop when fallback provider shown

[vignesh07]

Summary

When all providers are disabled, the fallback provider (.codex) would still trigger animation because:

• isVisible(.codex) returned true (fallback)
• But hasData was false (no fetch ever ran)
• So shouldAnimate() returned true → 60fps animation loop forever

This caused unnecessary CPU usage and battery drain.

The Fix (5 lines)

// Don't animate for fallback provider - it's only shown as a placeholder
// when nothing is enabled. Animating the fallback causes unnecessary
// CPU usage (battery drain). See #269, #139.
let isEnabled = self.isEnabled(provider)
let isFallbackOnly = !isEnabled && self.fallbackProvider == provider
if isFallbackOnly { return false }

Testing

Added BatteryDrainDiagnosticTests.swift with tests that verify:

• ✅ Animation driver should be nil when all providers disabled
• ✅ Animation driver should be nil when provider has data
• ✅ Idle state should have no active animation or refresh

Fixes #269, #139

[steipete]

Landed via temp rebase onto main.\n\n- Gate: pnpm lint && pnpm build && pnpm test\n- Land commit: f7ba013\n- Merge commit: b1b42f0\n\nThanks @vignesh07!