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.

scripts/lib.sh

@@ -23,11 +23,6 @@ read_packages() {
     grep -v '^\s*#' "$1" | grep -v '^\s*$'
 }
 
-confirm() {
-    read -r -p "$1 [y/N] " response
-    [[ "$response" =~ ^[yY]$ ]]
-}
-
 # --- Prerequisite checks ---
 
 check_not_root() {