fix(ads): grant rewards only after rewarded ad success

[evan188199-tech]

Summary

• Grant a rewarded-ad reward only after the SDK reports both successful status and reward.
• Treat a missing/blocked SDK, failed callback, or 30-second timeout as an error.
• Keep the dialog open on failure and offer retry; late success callbacks after a timeout cannot grant the reward.
• Add a focused reducer test covering idle, loading, success, failure, blocked, timeout, late callbacks, and retry.

Closes #242

Notes

Premium entitlement, purchase, and subscription behavior is unchanged.

Tests

• pnpm install --frozen-lockfile
• pnpm test
• pnpm exec tsc --noEmit
• Targeted ESLint check
• git diff --check

[vercel]

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[evan188199-tech]

@Snouzy Could you please approve the fork workflow run and take a look when you have a chance? The branch is rebased on the latest main, and local pnpm test, pnpm exec tsc --noEmit, targeted ESLint, and git diff --check all pass.