Allow chats when free-plan credits remain by removing post-generation hard block

[Abdulmuiz44]

Motivation

• Users with remaining monthly free credits were still seeing the upgrade/modal because a post-generation gate rejected responses when a single request's tokenCost exceeded the remaining credits.
• The intended behavior is to allow conversations while any credits remain and only show the upgrade modal when the user's remaining credits are zero.

Description

• Removed the post-generation hard check that returned an error when tokenCost > creditsRemaining from app/actions/generate.ts.
• Kept the pre-request credit cap check (creditsRemaining <= 0) intact so blocking still occurs when a user truly has no credits.
• This change aligns server-side gating with the profile UI which reports remaining credits.

Testing

• Ran type checking with npm run type-check (which executes tsc --noEmit -p tsconfig.typecheck.json) and it succeeded.

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Codex Task