feat: v1.4.1 — one-liner installer (opt-in, SHA-pinned)

[notabotchef]

Summary

Phase 3 of setup-friction-fix: opt-in one-liner installer for users who want a single command. Quick Start (v1.4.0) remains the default and recommended path.

• install.sh — full arg parser (--dry-run, --yes, --path, --mode=docker|manual, --verbose). 5-second countdown + Y/n confirm when not piped with --yes. NO_COLOR-aware. Idempotent — skips if already installed at the same version.
• A0 install dir auto-detection — checks 5 candidate paths + introspects running container mounts via docker inspect. BLOCKs ambiguously on multiple matches under --yes.
• SHA256 verification — _download_and_verify_override checks the override file SHA against a pinned value baked into the script per release. SHA mismatch → exit 3, file removed. Pinned SHA published in GitHub Release notes per tag.
• Two install modes — --mode=docker (default: download override, verify SHA, restart compose) and --mode=manual (git clone/pull + docker exec execute.py).
• Post-install check — runs bridge_doctor --quiet in the container. On failure, falls through to verbose output and links the Troubleshooting README section.
• .github/workflows/release.yml — on v* tag, computes install.sh SHA256 and attaches it to the GitHub Release notes. Publishes install.sh + docker-compose.override.yml as release assets.
• README "Install via script" section — placed after Quick Start, before Manual Install. Explicit security warning. Two equivalent forms: pipe direct vs download/inspect/run.

Polish (over autopilot phase commit)

• --help now uses awk to skip the shebang and stop at the first non-comment line. macOS-compatible (no GNU sed \? extension).
• Compose restart uses explicit (cd <dir> && docker compose up -d) when a docker-compose.yml is found, instead of an || fallback chain that ate stderr from the first attempt.

Why

Some users want curl-pipe-bash. Some users (correctly) refuse to. This PR ships the convenience without forcing it: Quick Start is documented first, the script is opt-in with explicit security warnings, and SHA pinning gives auditors a verifiable handshake.

Test plan

• bash -n install.sh — clean
• shellcheck install.sh — 0 errors
• bash install.sh --dry-run --yes — exit 0, no filesystem changes
• bash install.sh --path=/tmp/doesnotexist — exit 2, clear error
• bash install.sh --help — prints clean help (no shebang, no leading # )
• python -m pytest tests/test_probe_novnc.py — 7/7 pass (no regression)
• Deferred to user: real install on a fresh A0 instance — first v1.4.1 tag triggers release.yml and pins the SHA into the release notes

Files

• install.sh — 443 lines, opt-in installer
• .github/workflows/release.yml — SHA-pinned release notes
• README.md — "Install via script" section
• plugin.yaml — version 1.4.1

Phase 3 of 3 in .rune/plan-setup-friction-fix.md. Depends on #1 (v1.3.0) and #2 (v1.4.0).

[notabotchef]

SHA verification on the override file is a nice touch. The 5-second countdown for piped-from-curl is good UX — gives people a chance to ctrl-c if they didn't mean to run it.