docs: link every client in the clients-page chooser + correctness sweep

The "Which should I use?" table on the clients page listed most client
names as bold text, not links — only the Decky plugin and pf-webos were
clickable — so the client references appeared broken. Link each client to
its section (or dedicated page), and fix a stale Windows headless command.

Repo-wide docs correctness/staleness pass against the code:
- steam-deck: client-not-found -> flatpak-not-found (the real backend code)
- install: host cert is punktfunk-host-windows_<ver>.cer, not ..._setup.cer
- configuration: GPU_PRIORITY_CLASS default is auto; 10BIT/444 are default-on
- how-it-works/index: GameStream/Moonlight is opt-in (--gamestream)
- roadmap: clipboard sync is shipped, not planned
- install-client: MSIX/cert artifacts are arch-suffixed (_x64/_arm64)
- requirements: fix garbled 22H2/IddCx sentence
- status: Linux encode also covers AMD/Intel (VAAPI/Vulkan Video)
- automation: add the plugins.changed event
- windows-host: note the optional bundled VB-CABLE virtual mic
- sway: PUNKTFUNK_COMPOSITOR=hyprland is a wlroots-family alias
- running-as-a-service: punktfunk-probe is a source-build-only dev tool

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

docs-site/content/docs/steam-deck.md

@@ -28,7 +28,7 @@ You need three things on the Deck:
    ```
 
    (Full options: [Install a Client → Steam Deck](/docs/install-client#steam-deck). Without it, the
-   panel's **Stream** button reports `client-not-found`.)
+   panel's **Stream** button reports `flatpak-not-found`.)
 3. **A punktfunk host** running on your LAN — see [Install the Host](/docs/install). The Deck finds
    it automatically over mDNS, so nothing to configure here.
 
@@ -103,7 +103,7 @@ The plugin check follows the [channel](/docs/channels) you installed from: a plu
 
 | Symptom | Fix |
 |---|---|
-| **Stream** shows `client-not-found` | Install the client Flatpak in Desktop Mode (see [Before you start](#before-you-start)). |
+| **Stream** shows `flatpak-not-found` | Install the client Flatpak in Desktop Mode (see [Before you start](#before-you-start)). |
 | No hosts listed | Make sure the host is running and on the **same LAN**; the Deck needs `avahi` (shipped on SteamOS). Tap **Refresh**. |
 | Pairing fails / "not armed" | The PIN is shown only after you **arm pairing on the host**. Arm it, then enter the PIN within the window. |
 | Stream launches but doesn't focus | Start it from the panel (not by launching the Flatpak by hand) so Steam/gamescope focuses it. |