ci: [TOOL-838] release multi-arch image to ECR on tag push; drop Docker Hub workflow

[eculver]

Context

This fork now carries the pool-leak fix (#1) and dependency/base-image bumps (#2), and the plan (Linear TOOL-838) is for the fork to publish its own image to sfcompute's private ECR, replacing both the inherited Docker Hub workflow here and the monorepo's build-from-pinned-upstream-SHA workflow.

Changes

• Add .github/workflows/release.yml: builds a multi-arch (amd64+arm64) image and pushes to ECR sfcompute/postgres-mcp on v* tag pushes, via GitHub OIDC (ECR_PUSH_ROLE_ARN / AWS_REGION repo variables). workflow_dispatch runs are dry-run builds unless push=true is set.
• Delete .github/workflows/docker-build-dockerhub.yml: inherited from upstream; it pushes to crystaldba's Docker Hub with credentials this fork doesn't have, so it can only fail.

build.yml (CI) is untouched.

Before the first release

1. Monorepo terraform adds the OIDC role scoped to this repo (companion PR in sfcompute/sfcompute).
2. Set repo Actions variables: ECR_PUSH_ROLE_ARN, AWS_REGION (us-west-1).
3. Tag v0.3.0-sfc.1 (convention: v<upstream-base>-sfc.N).

🤖 Generated with Claude Code

[semanticdiff-com]

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Changed Files

File	Status
.github/workflows/docker-build-dockerhub.yml	0% smaller
.github/workflows/release.yml	0% smaller