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/status.md

@@ -3,9 +3,8 @@ title: "Status & Progress"
 description: "Where the work stands across the core, the host, and the native clients."
 ---
 
-A high-level view of where punktfunk stands. The full design lives in the
-[Implementation Plan](/docs/implementation-plan), the ordered plan of work in the
-[Roadmap](/docs/roadmap), and milestone-level detail in
+A high-level view of where punktfunk stands. The ordered plan of work is on the
+[Roadmap](/docs/roadmap), and milestone-level detail lives in
 [`CLAUDE.md`](https://git.unom.io/unom/punktfunk/src/branch/main/CLAUDE.md).
 
 ## Milestones at a glance