ci(compass): gate PRs on the dogfood e2e podman tier (SEA-1792)

[seal-agent]

Wire the deterministic full-stack e2e suite (go/e2e, //go:build podman) into
the GitHub Actions CI job as a required per-PR check, per the frozen design
record docs/designs/platform/compass-dogfood-e2e/design.md H8 + Decision D2.

Three steps after the pgtest guard: seed compass-agent:latest into local
containers-storage from the public GHCR image (EnsureImage present-checks the
local store, so no registry pull at test time; public per SEA-1690, no
credential); run go test -tags podman ./e2e/... with the same
capture-replay-exit shape as the pgtest step; then assert the suite ran rather
than podmanUsable-skipped, reading the skip substring from harness_test.go so
the guard can't drift vacuous. Landing this converts H3 (SEA-1787), H4 (the
5-leg capstone), and SEA-1359's non-Nix-host portability proof from
code-complete-unproven to proven by an actual run on a Nix-free ubuntu-latest
runner (podman 4.9.3).

Both end-state blockers are cleared (SEA-1690 GHCR publish Done; SEA-1691 uid
lift merged), so this wires the GA end state (required per-PR) directly.

Refs SEA-1792

Co-authored-by: Matt Wilkinson matt@sealedsecurity.com

[linear-code]

SEA-1792

[seal-agent]

Superseded by #256, which re-authors this under compass ownership (compass CI moved into the compass agents' lane) and folds in the postgres-on-PATH fix (bare postgresql in devenv packages — the root cause of this PR's red), the orion-pattern per-PR image source (build-from-tree when image inputs changed, else pull :latest), the two reviewer findings you handed over (CGO_ENABLED on the e2e step; the load-bearing assert-ran skip-string guard kept), and a §H8 design-record sync. Closing in favor of #256. Thanks for the clean handoff and the grounded root-cause.