Add unreleased.md documenting development-only changes

https://claude.ai/code/session_01EzU13EL8D5Ud2ngQUKDj9e

docs/unreleased.md

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+# Unreleased changes
+
+Changes merged into `development` that have not yet been released to `main`.
+
+---
+
+## Untranslated content now visible in all categories
+
+**Status:** On `development`, pending release.
+
+### What was broken
+
+When the category system is enabled, a page or post file without a category suffix (e.g. `posts/my-post.md`) was silently assigned to the default category only. Switching to any other category caused those files to disappear from the navigation and from `posts-*` tag listings — even though no translated version existed. If you wrote English posts without a `.en.md` suffix, they simply vanished the moment a visitor switched language.
+
+### What it does now
+
+Files without a category suffix are treated as uncategorised — meaning they belong to every category, not just the default one. A post called `my-post.md` now appears in the nav and post lists regardless of which category is active. A post called `my-post.en.md` still appears only in the `en` category as before.
+
+Mixed situations work as expected: if you have both `my-post.md` and `my-post.nb.md`, the Norwegian variant is shown when the `nb` category is active, and the bare `my-post.md` is shown for every other category.
+
+### What changes in the build output
+
+After rebuilding a site with `mdcms build`, affected entries in `nav.yml` gain an `uncategorized: true` field:
+
+```yaml
+- file: posts/my-post.md
+  title: My Post
+  sort: 100
+  uncategorized: true
+```
+
+In `search.json`, these entries carry `"category": null` instead of the default category code. This is what tells the renderer to include them universally.
+
+A rebuild is required for existing sites to pick up the change.