docs(site): add Windows host install, restructure nav, new public roadmap

- install (host): add a Windows (NVIDIA) section with signed-installer and
  certificate-trust steps; note the .cer is the same across releases.
- install-client: clarify the Windows MSIX certificate is the same every
  release (trust once, updates need nothing).
- Move "Project & Internals" out of the public docs site: relocate
  implementation-plan, apple-stage2-presenter, gamescope-multiuser,
  dualsense-haptics, ci, and gamestream-host-plan to docs/; drop them from
  the nav. Move windows-host into Host Setup.
- Rewrite roadmap as a lean public page with an at-a-glance grid and
  current statuses (Windows host shipped/beta, Apple incl. tvOS shipped,
  Android shipped, concurrent sessions + delegated pairing done).
- Fix status.md link to the now-internal implementation plan.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

docs-site/content/docs/install-client.md

@@ -71,7 +71,9 @@ certificate, so you import that certificate once before Windows will install the
 
 1. Open the [packages page](https://git.unom.io/unom/-/packages) (generic group), find
    **`punktfunk-client-windows`**, and download the newest **`.msix`** and its matching **`.cer`**.
-2. In an **admin** PowerShell, trust the publisher certificate (one-time), then install:
+2. **Trust the publisher certificate**, then install. The MSIX won't install until the certificate is
+   trusted — but it's the **same certificate for every release**, so this is genuinely one-time and
+   later updates need nothing. In an **admin** PowerShell:
 
    ```powershell
    Import-Certificate -FilePath .\punktfunk-client-windows.cer `