fix: audit MEDIUM fixes — merge fallback, service hardening, CI token

- moonarch-waybar: on merge failure, remove the stale output so waybar
  falls back to the system config (previously it kept running with stale
  merged data despite the error notification claiming otherwise).
- moonarch-doctor: hoist INSTALLED assignment above both OFFICIAL and AUR
  blocks so the script survives set -u when only aur.txt is present.
- zshrc parse_git_branch: gate on git rev-parse and replace three grep
  subshells with bash pattern matching, cutting prompt latency from
  ~5 subprocesses per render to 2 (status + symbolic-ref).
- moonarch-batsaver.service: validate the threshold is an integer 1-100
  before writing to sysfs, add NoNewPrivileges and protection directives
  instead of relying on kernel validation alone.
- ci/act-runner/Dockerfile: drop the broad "pacman -Sy *" sudoers entry
  (only -S --needed is required by makepkg), and pin run.sh to
  act_runner:0.3.1 so it cannot drift ahead of the pinned binary.
- .gitea/workflows/update-pkgver.yaml: push via credential.helper=store
  with a chmod 600 temp file instead of `git -c http.extraHeader=...`,
  so the token no longer shows up in /proc/PID/cmdline.

ci/act-runner/Dockerfile

@@ -1,10 +1,10 @@
 FROM archlinux:base-devel
 RUN pacman -Sy --noconfirm git curl && pacman -Scc --noconfirm
-RUN useradd -m builder && echo "builder ALL=(ALL) NOPASSWD: /usr/bin/pacman -Sy *, /usr/bin/pacman -S --needed *" >> /etc/sudoers
+RUN useradd -m builder && echo "builder ALL=(ALL) NOPASSWD: /usr/bin/pacman -S --needed *" >> /etc/sudoers
 ADD https://gitea.com/gitea/act_runner/releases/download/v0.3.1/act_runner-0.3.1-linux-amd64 /usr/local/bin/act_runner
 RUN echo "a05b2103a7cc5617197da214eaa06a1055362f21f9f475eb7fbacb8344d86cf8  /usr/local/bin/act_runner" | sha256sum -c - \
     && chmod +x /usr/local/bin/act_runner
-COPY --from=gitea/act_runner:latest /usr/local/bin/run.sh /usr/local/bin/run.sh
+COPY --from=gitea/act_runner:0.3.1 /usr/local/bin/run.sh /usr/local/bin/run.sh
 RUN mkdir -p /data && chown builder:builder /data
 USER builder
 ENV HOME=/home/builder