## Summary

Fixes #63401.

Only payment errors originating from the Zed provider now use the Zed
free-usage-limit callout. Other providers use the existing Request
Failed display with their original message and no Zed upgrade button.
Telemetry follows the same distinction.

Rename the UI error variant to `ZedPaymentRequired` to make its scope
explicit. Add regression coverage for OpenRouter, OpenAI, and Anthropic
errors both with and without an HTTP status, plus the Zed upgrade path.

## Verification

- `cargo test -p agent_ui --lib conversation_view::tests`: 104 passed,
including both new regression tests.
- Rustfmt checks and `git diff --check` passed.
- Provided a temporary OpenCode payment-error override for manual
testing; the override has been removed and is not included in this PR.
- Corgi failed to link `clang_rt.osx`; the Cargo fallback succeeded.
Details were recorded in the requested local Corgi log.

Release Notes:

- Fixed payment errors from non-Zed model providers incorrectly
prompting users to upgrade to Zed Pro instead of displaying the original
provider error message.