feat: add AI budget policy and period deployment config (#25122)

Closes
https://linear.app/codercom/issue/AIGOV-283/add-deployment-config-for-ai-budget-policy-and-period

Adds `CODER_AI_BUDGET_POLICY` and `CODER_AI_BUDGET_PERIOD` deployment
options for AI Governance cost controls.

coderd/apidoc/docs.go

@@ -13802,6 +13802,13 @@ const docTemplate = `{
                         }
                     ]
                 },
+                "budget_period": {
+                    "type": "string"
+                },
+                "budget_policy": {
+                    "description": "Budget settings for AI Governance cost controls.",
+                    "type": "string"
+                },
                 "circuit_breaker_enabled": {
                     "description": "Circuit breaker protects against cascading failures from upstream AI\nprovider overload (503, 529).",
                     "type": "boolean"

coderd/apidoc/swagger.json

@@ -12278,6 +12278,13 @@
 						}
 					]
 				},
+				"budget_period": {
+					"type": "string"
+				},
+				"budget_policy": {
+					"description": "Budget settings for AI Governance cost controls.",
+					"type": "string"
+				},
 				"circuit_breaker_enabled": {
 					"description": "Circuit breaker protects against cascading failures from upstream AI\nprovider overload (503, 529).",
 					"type": "boolean"