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/roadmap.md

@@ -51,6 +51,8 @@ see [Status & Progress](/docs/status).
   (the encoder re-targets mid-stream when bitrate is set to Automatic).
 - **Surround sound** — 5.1 and 7.1 end to end: the host encodes multichannel via multistream Opus and
   the native clients render more than two channels, with clean, synchronous stereo where the path is stereo.
+- **Clipboard sync** — bidirectional **text and images** between host and client, carried on a side
+  plane over the native protocol's QUIC channel.
 
 ## 🟡 In progress
 
@@ -90,11 +92,11 @@ see [Status & Progress](/docs/status).
   rate and the client presents with tearing-control/VRR instead of a fixed cadence, for tear- and
   judder-free gaming. Builds on the client's presentation-feedback path and the per-session virtual
   outputs.
-- **Desktop quality-of-life.** The essentials that make remote *work* pleasant, each a new side plane
-  over the existing QUIC datagram channel: bidirectional rich **clipboard sync** (text and images),
-  **multi-monitor streaming** (present the host's several outputs as separate client windows), and
-  **virtual-webcam redirection** (the client's camera shows up as a webcam on the host, so video calls
-  run on the remote machine).
+- **Desktop quality-of-life.** More of the essentials that make remote *work* pleasant, each a new side
+  plane over the existing QUIC datagram channel: **multi-monitor streaming** (present the host's several
+  outputs as separate client windows) and **virtual-webcam redirection** (the client's camera shows up
+  as a webcam on the host, so video calls run on the remote machine). *(Clipboard sync already shipped —
+  see above.)*
 
 ## ⛔ Parked / blocked