feat(codersdk): add circuit breaker configuration support for aibridge (#21546)

## Summary

Add circuit breaker support for AI Bridge to protect against cascading
failures from upstream AI provider rate limits (HTTP 429, 503, and
Anthropic's 529 overloaded responses).

## Changes

- Add 5 new CLI options for circuit breaker configuration:
  - `--aibridge-circuit-breaker-enabled` (default: false)
  - `--aibridge-circuit-breaker-failure-threshold` (default: 5)
  - `--aibridge-circuit-breaker-interval` (default: 10s)
  - `--aibridge-circuit-breaker-timeout` (default: 30s)
  - `--aibridge-circuit-breaker-max-requests` (default: 3)
- Update aibridge dependency to include circuit breaker support
- Add tests for pool creation with circuit breaker providers

## Notes

- Circuit breaker is **disabled by default** for backward compatibility
- When enabled, applies to both OpenAI and Anthropic providers
- Uses sony/gobreaker internally via the aibridge library

## Testing

```
make test RUN=TestPoolWithCircuitBreakerProviders
```

docs/reference/cli/server.md

@@ -1847,6 +1847,17 @@ Maximum number of AI Bridge requests per second per replica. Set to 0 to disable
 
 Emit structured logs for AI Bridge interception records. Use this for exporting these records to external SIEM or observability systems.
 
+### --aibridge-circuit-breaker-enabled
+
+|             |                                                      |
+|-------------|------------------------------------------------------|
+| Type        | <code>bool</code>                                    |
+| Environment | <code>$CODER_AIBRIDGE_CIRCUIT_BREAKER_ENABLED</code> |
+| YAML        | <code>aibridge.circuitBreakerEnabled</code>          |
+| Default     | <code>false</code>                                   |
+
+Enable the circuit breaker to protect against cascading failures from upstream AI provider rate limits (429, 503, 529 overloaded).
+
 ### --aibridge-proxy-enabled
 
 |             |                                            |