feat: convert soft_limit to limit (#22048)

In relation to
[`internal#1281`](https://github.com/coder/internal/issues/1281)

Remove the `soft_limit` field from the `Feature` type and simplify
license limit handling. This change:

- Removes the `soft_limit` field from the API and SDK
- Uses the soft limit value as the single `limit` value in the UI and
API
- Simplifies warning logic to only show warnings when the limit is
exceeded
- Updates tests to reflect the new behavior
- Updates the UI to use the single limit value for display

coderd/apidoc/docs.go

@@ -15368,10 +15368,6 @@ const docTemplate = `{
                 "limit": {
                     "type": "integer"
                 },
-                "soft_limit": {
-                    "description": "SoftLimit is the soft limit of the feature, and is only used for showing\nincluded limits in the dashboard. No license validation or warnings are\ngenerated from this value.",
-                    "type": "integer"
-                },
                 "usage_period": {
                     "description": "UsagePeriod denotes that the usage is a counter that accumulates over\nthis period (and most likely resets with the issuance of the next\nlicense).\n\nThese dates are determined from the license that this entitlement comes\nfrom, see enterprise/coderd/license/license.go.\n\nOnly certain features set these fields:\n- FeatureManagedAgentLimit",
                     "allOf": [

coderd/apidoc/swagger.json

@@ -13895,10 +13895,6 @@
 				"limit": {
 					"type": "integer"
 				},
-				"soft_limit": {
-					"description": "SoftLimit is the soft limit of the feature, and is only used for showing\nincluded limits in the dashboard. No license validation or warnings are\ngenerated from this value.",
-					"type": "integer"
-				},
 				"usage_period": {
 					"description": "UsagePeriod denotes that the usage is a counter that accumulates over\nthis period (and most likely resets with the issuance of the next\nlicense).\n\nThese dates are determined from the license that this entitlement comes\nfrom, see enterprise/coderd/license/license.go.\n\nOnly certain features set these fields:\n- FeatureManagedAgentLimit",
 					"allOf": [