feat: audit group AI budget mutations (#25374)

Relates to
https://linear.app/codercom/issue/AIGOV-284/add-group-budgets-table-and-crud-api

Adds audit-log support for `group_ai_budget` mutations. Without it, an
admin could silently lower a spend limit from `$500` to `$50` or delete
a budget entirely, with no record of who performed the action.

Both write (`create-or-update`) and delete actions now produce audit log
entries, including before/after diffs for `spend_limit_micros`.

Depends on #25203.

## Old Version
<img width="1340" height="456" alt="image"
src="https://github.com/user-attachments/assets/e9ff52fb-a905-4aef-a4ee-7cdc58e68b75"
/>

## New Version (see
https://github.com/coder/coder/pull/25374/changes/9d22833de87cc106c24142c1d471a3f71872bf67)
<img width="1347" height="496" alt="image"
src="https://github.com/user-attachments/assets/1b9bbfa1-f86d-48e3-a0b1-266eb76f851f"
/>

coderd/apidoc/docs.go

@@ -21804,6 +21804,7 @@ const docTemplate = `{
                 "ai_seat",
                 "ai_provider",
                 "ai_provider_key",
+                "group_ai_budget",
                 "chat",
                 "user_secret"
             ],
@@ -21837,6 +21838,7 @@ const docTemplate = `{
                 "ResourceTypeAISeat",
                 "ResourceTypeAIProvider",
                 "ResourceTypeAIProviderKey",
+                "ResourceTypeGroupAIBudget",
                 "ResourceTypeChat",
                 "ResourceTypeUserSecret"
             ]

coderd/apidoc/swagger.json

@@ -20006,6 +20006,7 @@
 				"ai_seat",
 				"ai_provider",
 				"ai_provider_key",
+				"group_ai_budget",
 				"chat",
 				"user_secret"
 			],
@@ -20039,6 +20040,7 @@
 				"ResourceTypeAISeat",
 				"ResourceTypeAIProvider",
 				"ResourceTypeAIProviderKey",
+				"ResourceTypeGroupAIBudget",
 				"ResourceTypeChat",
 				"ResourceTypeUserSecret"
 			]