docs(env): stop teaching the compositor pin + uid-1000 anchors in starters

Field triage (Nobara, Discord): the kde.md starter host.env told desktop
users to set PUNKTFUNK_COMPOSITOR=kwin, which PINS the backend — detect()
short-circuits and the capture-loss rebuild never re-detects — so a
mid-stream switch to Game Mode killed the stream instead of following it.
A follow-up hardcoded XDG_RUNTIME_DIR=/run/user/1000 anchor broke PipeWire
for any non-1000 uid (pw audio connect: Creation failed).

Revamp across every starter/example/reference:
- Desktop starters (kde/gnome/hyprland/sway) shrink to
  PUNKTFUNK_VIDEO_SOURCE=virtual + an explicit warning that pinning
  disables session-following; forcing a backend is CI/appliance-only.
- host.env.example: rewritten around auto-detection; anchors demoted to a
  commented ssh/cron-only block with the uid trap spelled out; the
  gamescope ATTACH/MANAGED knobs documented (previously missing);
  case-sensitivity called out.
- packaging/bazzite/host.env + README: drop the uid-1000 anchors (a
  systemctl --user service inherits/derives them); README's stale
  PUNKTFUNK_COMPOSITOR=gamescope-era template synced to the real one.
- packaging/kde/host.env: loud APPLIANCE-ONLY header (it pins on purpose).
- configuration.md: session-anchors section inverted to "leave unset",
  compositor row states the pin consequence, case-sensitivity note.
- troubleshooting.md: new "session fails right after editing host.env"
  section (case, wrong-uid anchors, stale pin, restart-to-apply).
- gamescope.md/bazzite.md: attach/managed descriptions match current
  behavior (managed is the infra-detected default; attach re-modes a
  box-owned session to the client's resolution).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

docs-site/content/docs/troubleshooting.md

@@ -103,7 +103,22 @@ See [GNOME](/docs/gnome) for the GL/EGL userspace details.
 - KWin must be **≥ 6.5.6** (`kwin_wayland --version`); GNOME **≥ 48**; gamescope **≥ 3.16.22**. See
   [KDE](/docs/kde) for the KWin/Wayland requirement and [gamescope](/docs/gamescope) for the
   gamescope one.
-- Confirm `PUNKTFUNK_COMPOSITOR` in [`host.env`](/docs/configuration) matches your desktop.
+- If [`host.env`](/docs/configuration) sets `PUNKTFUNK_COMPOSITOR`, **remove it** — the host
+  auto-detects the live compositor, and the pin points it at one backend even when a different
+  session is live (it also disables Gaming ↔ Desktop following).
+
+## Session fails right after editing host.env
+
+- Keys are **case-sensitive**: `punktfunk_gamescope_attach=1` sets nothing — use the exact
+  uppercase names.
+- Hardcoded session anchors with the wrong uid (`XDG_RUNTIME_DIR=/run/user/1000` when `id -u`
+  isn't 1000) point the host at another user's PipeWire/D-Bus: audio errors like
+  `pw audio connect … Creation failed`, no capture, and clients reporting the host as
+  unreachable or asleep. **Delete both anchor lines** — a `systemctl --user` service doesn't need
+  them — or fix the uid.
+- `PUNKTFUNK_COMPOSITOR` pins the backend and disables Gaming ↔ Desktop following — remove it on
+  any box that switches sessions.
+- The env file is read at service start: `systemctl --user restart punktfunk-host` after edits.
 
 ## Capture fails: "Session creation inhibited" (GNOME)