docs: user-facing docs revamp — structured product docs + per-platform setup

Replace the dev/agent-log pages with a proper user-facing doc set:

- Getting Started: Introduction (rewritten), How It Works, Quick Start.
- Host Setup: Requirements, then clean per-platform guides — Ubuntu GNOME,
  Ubuntu KDE, Fedora KDE (new), Bazzite (rewritten) — plus Running as a Service
  (desktop / headless GNOME / headless KDE).
- Connecting: Clients overview, Moonlight, Pairing & Trust.
- Configuration: host.env reference, Host CLI, Troubleshooting.
- The dev/design notes (architecture, roadmap, the deferred design specs, CI)
  move to a clearly-separated "Project & Internals" nav section.

Removes the superseded box-specific pages (gnome-box, headless-box, linux-setup,
overview). status.md (the internal progress tracker, with box IPs) is kept as a
file but dropped from the public nav. Site builds clean.

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

docs-site/content/docs/meta.json

@@ -2,19 +2,29 @@
   "title": "Documentation",
   "pages": [
     "index",
-    "overview",
-    "status",
-    "implementation-plan",
+    "how-it-works",
+    "quickstart",
+    "---Host Setup---",
+    "requirements",
+    "ubuntu-gnome",
+    "ubuntu-kde",
+    "fedora-kde",
+    "bazzite",
+    "running-as-a-service",
+    "---Connecting---",
+    "clients",
+    "moonlight",
+    "pairing",
+    "---Configuration---",
+    "configuration",
+    "host-cli",
+    "troubleshooting",
+    "---Project & Internals---",
     "roadmap",
-    "m2-plan",
+    "implementation-plan",
+    "windows-host",
     "apple-stage2-presenter",
     "gamescope-multiuser",
-    "---Setup---",
-    "linux-setup",
-    "headless-box",
-    "gnome-box",
-    "bazzite",
-    "windows-host",
     "dualsense-haptics",
     "ci"
   ]