chore: Stop stamping the router image into the gateway bundle

[privateip]

Summary

The publish workflow still stamps the galactic-router image tag into the gateway's Kustomize base, which has run one container since galactic-router moved to its own DaemonSet.

The stamp matches nothing, so it does no harm, but its comment misdescribes the gateway pod and two architecture docs repeat the claim.

This removes the stamp and its comment, and corrects both docs.

Test plan

• The gateway base still renders only the galactic-gateway image before publish
• The published bundle's gateway base still carries the versioned galactic-gateway image

Fixes #701

🤖 Generated with Claude Code

[privateip]

pr-adversary: merge. No findings. The removed stamp matched nothing, since the gateway base is single-container with only the galactic-gateway image.

pr-conventions-reviewer: hold (waived by user decision). Title is 61 characters, over 50, but pr-conventions allows 72. Summary names components and test plan item added to body, both waived as non-blocking. Overlap with #745, #747, #738 in ARCHITECTURE-GATEWAY.md resolved: hunks sit at lines 778+, 40, 109 apart from this PR's deletion at line 772, so merge order is not blocking.

No code changes applied; the PR body was already updated as reviewed.

CI: All checks passed (Lint, Build, Unit Tests, Unit Tests (root), E2E Tests, image publish jobs, CLA).

Merge method: merge, enabled via auto-merge. The ruleset requires 1 code-owner approval and last-push approval; auto-merge will wait for human approval before completing.