ci: skip self-test when pihole missing; remove stale audit and copilot automerge workflow

[TimInTech]

Motivation

• Remove stale/generated repository artifacts that are not needed (.audit/report.yaml).
• Remove the copilot-only automerge workflow to avoid unexpected automatic merges for copilot/* branches.
• Prevent CI failures on GitHub runners that do not have the Pi-hole CLI installed by making the self-test optional.

Description

• Deleted .audit/report.yaml which contained a generated audit report and is no longer required.
• Deleted .github/workflows/yaml-automerge-pilot.yml to remove the copilot automerge automation.
• Updated .github/workflows/ci-sanity.yml so the script self-test first runs bash -n and then only executes the real self-test when pihole is present by checking command -v pihole >/dev/null 2>&1, otherwise it prints a skip message.

Testing

• bash -n pihole_maintenance_pro.sh was run and returned success (no syntax errors).
• shellcheck -x pihole_maintenance_pro.sh scripts/*.sh tools/*.sh could not be executed because shellcheck is not installed in the environment (unavailable).
• shfmt -d . could not be executed because shfmt is not installed in the environment (unavailable).
• Running the self-test RUN_SELFTEST=1 bash pihole_maintenance_pro.sh --no-apt --no-upgrade --no-gravity --no-dnsreload failed locally due to the pihole CLI being absent, which is why the CI change skips the self-test when pihole is missing.

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Codex Task