Align CI with centralized E2E workflow

[casey-brooks]

Summary

• Aligns E2E workflow with centralized architecture: provision via agynio/bootstrap/.github/actions/provision@main, deploy agynd-cli from source with devspace dev, then run agynio/e2e/.github/actions/run-tests@main.
• Removes repo-local E2E execution, Codex install, ad hoc agn-cli checkout, and local test env overrides from the PR workflow.
• Adds read-only workflow permissions to CI/E2E.
• Updates DevSpace source deploy to use the unpinned buf.build/agynio/api module instead of a pinned API commit.
• Verified PR workflows do not build or publish images/charts and do not override bootstrap cluster environment.

Closes #123

Test & Lint Summary

• actionlint .github/workflows/ci.yml .github/workflows/e2e.yml .github/workflows/release.yml — passed with no errors.
• yamllint -d '{extends: default, rules: {line-length: disable, document-start: disable, truthy: disable}}' .github/workflows/ci.yml .github/workflows/e2e.yml .github/workflows/release.yml devspace.yaml — passed with no errors.
• buf generate buf.build/agynio/api --path agynio/api/gateway/v1 --include-imports — passed.
• gofmt -w $(find cmd internal test -name '*.go' -print) — passed with no changes.
• go test ./... — 7 packages passed, 0 failed, 0 skipped.
• go build ./... — passed.
• devspace print --debug — passed.

[casey-brooks]

Test & Lint Summary

• actionlint .github/workflows/ci.yml .github/workflows/e2e.yml .github/workflows/release.yml — passed with no errors.
• yamllint -d '{extends: default, rules: {line-length: disable, document-start: disable, truthy: disable}}' .github/workflows/ci.yml .github/workflows/e2e.yml .github/workflows/release.yml devspace.yaml — passed with no errors.
• buf generate buf.build/agynio/api --path agynio/api/gateway/v1 --include-imports — passed.
• gofmt -w $(find cmd internal test -name '*.go' -print) — passed with no changes.
• go test ./... — 7 packages passed, 0 failed, 0 skipped.
• go build ./... — passed.
• devspace print --debug — passed.