cleanup: remove invented zsh override layer, harden moondoc

Earlier ClaudeCode sessions had wired a `~/.zshrc.d/*.zsh` snippet loop
plus a `~/.zshrc.local` fallback into defaults/shell/zshrc and made
post-install.sh create the directory unconditionally — neither is a zsh
convention nor documented anywhere. Remove both, simplify post-install
to write only `source /etc/zsh/zshrc.moonarch`, drop stale rustup
next-step hint, drop dead `confirm()` in lib.sh (orphan since
transform.sh deletion 2026-04-21).

moonarch-doctor: replace useless existence checks (zshrc.moonarch,
/usr/share/moonarch/) with real signal. User-service and helper-script
lists now derive from `pacman -Qql moonarch-git` (drift-proof) plus an
explicit list of post-install-enabled externals (currently `stasis`).
New udev-effectiveness check for charge_control_end_threshold —
verifies group=wheel + group-writable, surfaces broken rules instead
of staying silent.

Translate two German ABOUTME comments (moonarch-waybar-cpugov,
moonarch-waybar-gpustat) to English for consistency.

defaults/bin/moonarch-waybar-gpustat

@@ -1,6 +1,6 @@
 #!/usr/bin/bash
-# ABOUTME: Waybar-Modul das die GPU-Auslastung als JSON ausgibt.
-# ABOUTME: Wird von der Waybar custom/gpu-usage Config referenziert.
+# ABOUTME: Waybar module that outputs GPU utilization as JSON.
+# ABOUTME: Referenced by the Waybar custom/gpu-usage config.
 
 GPU_STAT=$(cat /sys/class/hwmon/hwmon*/device/gpu_busy_percent 2>/dev/null | head -1 || echo "0")
 GPU_STAT="${GPU_STAT:-0}"