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

docs/reference/api/enterprise.md

@@ -329,7 +329,6 @@ curl -X GET http://coder-server:8080/api/v2/entitlements \
       "enabled": true,
       "entitlement": "entitled",
       "limit": 0,
-      "soft_limit": 0,
       "usage_period": {
         "end": "2019-08-24T14:15:22Z",
         "issued_at": "2019-08-24T14:15:22Z",
@@ -341,7 +340,6 @@ curl -X GET http://coder-server:8080/api/v2/entitlements \
       "enabled": true,
       "entitlement": "entitled",
       "limit": 0,
-      "soft_limit": 0,
       "usage_period": {
         "end": "2019-08-24T14:15:22Z",
         "issued_at": "2019-08-24T14:15:22Z",