test(e2e): remove schema parity campaign

[elezar]

Summary

Remove the completed schema-v1/schema-v2 parity campaign while retaining unique current-product regression coverage in the regular gateway configuration tests.

Related Issue

Follow-up cleanup for #2792.

Stack

• This PR removes the completed parity campaign.
• test(conformance): run driver suites with cargo #3866 is stacked on this PR and moves driver conformance execution to Cargo tests.

Changes

• Remove the parity harness, task definitions, historical campaign manifests and results, and verifier-specific Python tests.
• Simplify the Podman E2E configuration generator and remove parity-only environment, digest, provenance, and capture plumbing.
• Remove the unused in-tree OPENSHELL_PODMAN_HOST_GATEWAY_IP and OPENSHELL_PODMAN_USERNS overrides in favor of the documented Podman TOML fields.
• Move durable current-schema assertions for in-tree and external Podman configuration into test:gateway-config.
• Remove test:e2e-parity from the aggregate test task and update testing, architecture, Windows, and agent documentation.

Testing

• mise run --jobs 1 pre-commit passes after rebasing onto current main
• mise run test:gateway-config
• Focused Python configuration and release-formula tests (12 passed)
• Focused Podman driver configuration tests (73 passed)
• cargo test --locked --package openshell-gateway reaches linking but cannot complete locally because the system z3 library is unavailable
• Live E2E tests were not run; lifecycle coverage remains in the regular driver E2E suites

Checklist

• Follows Conventional Commits
• Commits are signed off (DCO)

[github-actions]

🌿 Preview your docs: https://nvidia-preview-pr-3864.docs.buildwithfern.com/openshell

[krishicks]

Analysis by agent found one cleanup item I think is worth addressing at some point:

podman_config in crates/openshell-gateway/src/lib.rs reads OPENSHELL_PODMAN_HOST_GATEWAY_IP and OPENSHELL_PODMAN_USERNS from the environment. After this PR, nothing in the repo sets them and they are undocumented. The last mention was e2e/parity/test.sh, which set them only to verify they were ignored.

Options: document them alongside OPENSHELL_PODMAN_SOCKET in container-deployment.mdx, or remove them in favour of TOML config.

[elezar]

Addressed in 7a80252. The in-tree gateway no longer reads OPENSHELL_PODMAN_HOST_GATEWAY_IP or OPENSHELL_PODMAN_USERNS; the documented Podman TOML fields remain the canonical configuration. OPENSHELL_PODMAN_SOCKET is retained because the E2E wrapper still uses that override.