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
```

coderd/apidoc/docs.go

@@ -12038,6 +12038,22 @@ const docTemplate = `{
                 "bedrock": {
                     "$ref": "#/definitions/codersdk.AIBridgeBedrockConfig"
                 },
+                "circuit_breaker_enabled": {
+                    "description": "Circuit breaker protects against cascading failures from upstream AI\nprovider rate limits (429, 503, 529 overloaded).",
+                    "type": "boolean"
+                },
+                "circuit_breaker_failure_threshold": {
+                    "type": "integer"
+                },
+                "circuit_breaker_interval": {
+                    "type": "integer"
+                },
+                "circuit_breaker_max_requests": {
+                    "type": "integer"
+                },
+                "circuit_breaker_timeout": {
+                    "type": "integer"
+                },
                 "enabled": {
                     "type": "boolean"
                 },

coderd/apidoc/swagger.json

@@ -10690,6 +10690,22 @@
 				"bedrock": {
 					"$ref": "#/definitions/codersdk.AIBridgeBedrockConfig"
 				},
+				"circuit_breaker_enabled": {
+					"description": "Circuit breaker protects against cascading failures from upstream AI\nprovider rate limits (429, 503, 529 overloaded).",
+					"type": "boolean"
+				},
+				"circuit_breaker_failure_threshold": {
+					"type": "integer"
+				},
+				"circuit_breaker_interval": {
+					"type": "integer"
+				},
+				"circuit_breaker_max_requests": {
+					"type": "integer"
+				},
+				"circuit_breaker_timeout": {
+					"type": "integer"
+				},
 				"enabled": {
 					"type": "boolean"
 				},