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>

packaging/bazzite/host.env

@@ -3,10 +3,9 @@
 # The compositor + input backend are AUTO-DETECTED per connect from the ACTIVE session: the host
 # follows the box as you flip between Steam Gaming Mode (gamescope — a managed session at the
 # CLIENT's resolution) and a KDE/GNOME Desktop (KWin/Mutter virtual output at the client's mode).
-# So nothing here forces a backend — only the trustworthy anchors stay.
-
-XDG_RUNTIME_DIR=/run/user/1000
-DBUS_SESSION_BUS_ADDRESS=unix:path=/run/user/1000/bus
+# So nothing here forces a backend, and no session anchors are needed: a `systemctl --user`
+# service inherits the correct XDG_RUNTIME_DIR and the host derives the bus from it. (Keys are
+# CASE-SENSITIVE — use the exact uppercase names.)
 
 PUNKTFUNK_VIDEO_SOURCE=virtual
 
@@ -23,10 +22,11 @@ PUNKTFUNK_VIDEO_SOURCE=virtual
 #
 # GAME MODE = ATTACH (the box owns its session; the host follows). The box decides whether it's in
 # Steam Gaming Mode or a Desktop — you switch with the normal Steam UI / "Switch to Desktop". The
-# host just ATTACHES to whatever's live and captures it; it never tears the session down or relaunches
-# it. So switching Desktop<->Game is rock-solid, and when you disconnect the box STAYS in its current
-# mode — reconnecting drops you right back where you were. The streamed resolution in game mode is the
-# box's gamescope mode (see SCREEN_WIDTH/HEIGHT in /etc/gamescope-session-plus/sessions.d/steam).
+# host just ATTACHES to whatever's live and captures it; it never tears the session down. So
+# switching Desktop<->Game is rock-solid, and when you disconnect the box STAYS in its current
+# mode — reconnecting drops you right back where you were. On a resolution mismatch the host
+# restarts the box's own game-mode session at the CLIENT's resolution (a foreign/bare gamescope
+# instead streams at its own mode).
 PUNKTFUNK_GAMESCOPE_ATTACH=1
 #
 # Opt OUT to the MANAGED model instead (host tears the box's gamescope down on connect and launches