ci: run refactor canary from main

[Hweinstock]

Description

Problem

Scheduled and workflow_run triggers only fire on the default branch (docs), so aws#2503 and aws#2508 on refactor never run.

Solution

• Port refactor's E2E workflow as refactor-e2e.yml, always checking out refactor code.
• Add canary(refactor) with its own concurrency group.
• Port metrics workflow, triggered by canary(refactor).
• Split ref into artifactRef/testRef so the canary runs the latest refactor tests against the @rc build.

Notes

• Filename: refactor-e2e.yml avoids main's .github/workflows/e2e* path filter, which would otherwise trigger the full E2E suite on edits.
• Concurrency group: canary-refactor, since main's Canary already uses the canary group.
• No environment: matches refactor. Confirm the first run gets AWS credentials.
• Metric dimension: now WorkflowName=canary(refactor).

Related Issue

Follow-up to aws#2503 and aws#2508.

Type of Change

• Other (please describe): CI

Testing

Triggers can't run before merge. The test was a local simulation of the job: tests at refactor HEAD, with the RC commit built in artifact/.

> npx prettier --check .github/ && actionlint .github/workflows/{refactor-e2e,canary-refactor,workflow-metrics}.yml
All matched files use Prettier code style!
> node artifact/dist/index.js --version
1.0.0-rc.5
> AGENTCORE_CLI_PATH="node $PWD/artifact/dist/index.js" bunx vitest list --config vitest.e2e.config.ts --tagsFilter=canary
48 tests (harness.test.ts: 10, templates.test.ts: 38), 0 from artifact/

Checklist

• I have read the CONTRIBUTING document
• My changes generate no new warnings