Update changelogs from fern repo

fern/products/sdks/generators/typescript/changelog/2026-09-05.mdx

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+## 3.91.0
+**`(feat):`** Add the opt-in `deepObjectMapQueryParameters` configuration option. When enabled, query parameters typed
+as a map (e.g. `map<string, string>`, which is what an OpenAPI `type: object` + `additionalProperties`
+schema imports as) are handed to the query builder and serialized in deepObject form
+(`?metadata[env]=prod`) instead of being JSON-stringified (`?metadata=%7B%22env%22...`). Maps whose
+values are objects, nested maps, lists, sets, or date-times are supported too: with the serde layer
+enabled they are run through the generated schema first, so nested keys use wire names, sets become
+arrays, and dates are ISO strings (`?metadata[env][created_at]=2026-09-04T00:00:00.000Z`). Defaults to
+`false`, so existing SDKs are unaffected.
+
+```yaml
+- name: fernapi/fern-typescript-sdk
+  config:
+    deepObjectMapQueryParameters: true
+```
+
+Maps with `unknown` values (an OpenAPI `additionalProperties: true` import) are rejected at
+generation time. There is no schema to normalize such a value against, so a non-plain object like a
+`Date` or a `Set` would contribute no enumerable keys and be dropped from the query string with no
+error. Rather than emit an SDK that silently loses data, generation fails:
+
+```
+Query parameter 'metadata' on GET /search is a map with `unknown` values, which
+`deepObjectMapQueryParameters` cannot safely encode: a non-plain object such as a Date or a Set
+would be silently dropped from the query string.
+Either give the map a concrete value type (so the serde layer can normalize it), or disable
+`deepObjectMapQueryParameters`.
+```
+
+One other behaviour to be aware of, inherent to deepObject encoding: an empty map is omitted from the
+query string entirely, where it previously serialized as `?key=%7B%7D`. There are no keys to explode,
+so nothing is emitted.
+
+Query parameters explicitly declared `explode: false` keep their existing encoding; deepObject form is
+only applied where `explode` is true or unset.
+
+