feat: match the supervisor image to the gateway, allow pinning prerequisites

[vyncint]

Started as "should we allow selecting OpenShell / apple-container versions?" — and turned up a live version mismatch on the reference machine, which this PR fixes alongside the requested feature.

1. Bug: the supervisor image tag didn't track the gateway

--supervisor-image defaulted to a hardcoded …/supervisor:0.0.96, but OpenShell's installer resolves its own latest release. On the reference machine that meant:

	version
installed gateway	0.0.97
supervisor the driver used	0.0.96 (hardcoded)
supervisor:0.0.97 on the registry	exists (HTTP 200) — just unused

The supervisor runs inside every sandbox and speaks the gateway's protocol, so this is a silent protocol mismatch, and nothing detected or reported it. It happened to work (0.0.96 ↔ 0.0.97 are compatible) — luck, not design. update --all runs brew upgrade openshell, which can move the gateway independently at any time.

Fix: the driver reads openshell-gateway --version and uses the matching supervisor:<version>. The compute-driver contract carries no gateway version, and the driver shares the host with the gateway, so the binary is the only source. Guardrails:

• An explicit --supervisor-image / OSHL_AC_SUPERVISOR_IMAGE always wins (detected via flag.Visit + env lookup).
• If the matching tag is unpublished, the single extraction call site falls back to the pinned image and warns — a create cannot regress into failing outright.
• Shelling out is unsuitable for config.Parse, so resolution is an explicit call after parsing; forgetting it degrades to the pinned tag, never to an empty image.

2. Feature: pin the prerequisites

Only the driver's own release was selectable; OpenShell and apple/container always resolved to latest — installs weren't reproducible and a bad upstream release couldn't be rolled back. Both upstreams already support pinning, so this is pass-through:

curl -LsSf …/install.sh | sh -s -- --version v0.2.6 --openshell-version 0.0.97 --container-version 1.2.0
openshell-driver-applecontainer update --all --openshell-version 0.0.97 --container-version 1.2.0

• OpenShell: its installer honors OPENSHELL_VERSION. brew can't install an arbitrary tap version, so a pin routes through the official installer — downloaded to a file and run as sh <file>, not piped into a shell, so a truncated fetch can't execute as a partial script.
• apple/container: update-container.sh -v <ver>; the .pkg URL is already tag-based.
• Env mirrors: OSHL_AC_OPENSHELL_VERSION, OSHL_AC_CONTAINER_VERSION. Defaults stay "latest" so users keep getting fixes; pinning is opt-in.
• --openshell-version/--container-version without --all is rejected rather than silently ignored.

3. Visibility

setup now logs the resolved driver / gateway / apple-container versions and the supervisor image, and warns when the tag ≠ gateway. The README compatibility table said "pinned to v0.0.96", which no longer matched reality — corrected, and the pinning recipes documented.

Verification

• Live: setup logged matched the supervisor image to the installed gateway gateway_version=0.0.97, then a sandbox reached Ready on the derived image — cache shows supervisor-0.0.97-523e0565f895 alongside the old 0.0.96 — with exec returning kernel 6.18.15. Version summary printed driver / gateway 0.0.97 / apple_container 1.2.0 and no mismatch warning.
• Tests: supervisor resolution (matches gateway / respects explicit pin / falls back when unknown / Parse records explicitness) and version probing (gateway + container + v-prefix + junk + missing binary) with mismatch-warning assertions.
• go test -race ./..., golangci-lint (0 issues), shellcheck, make sec all clean. install.sh -h now prints the header robustly (it was about to leak set -eu as the header grew).

Also fixed while here: cleanup -d removes the supervisor image the driver actually uses, not just the pinned default.