fix(ci): keep the running API image when the web triggers a deploy

[jhosepmyr]

Description

Follow-up to #46: when a push to main triggers the reqsai-infra MVP deploy, pass api_ref=keep so only the web is rebuilt and the running API image is left untouched. Before, the API ref defaulted to main, so the first web release would have redeployed the API from its main (still from July) and rolled it back.

Feature module / area: ci

Related issue / US: continuous deployment of the MVP (reqsai-infra PR #7)

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Type of Change

• feat — new feature or UI component
• fix — bug fix
• refactor — code change without behavior change
• test — tests only
• docs — documentation only
• build / ci — build, dependencies, or CI/CD
• chore — maintenance

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Checklist

• The PR targets develop (not main)
• Branch name follows feature/*, bugfix/*, or hotfix/*
• Commits follow Conventional Commits
• bun run lint passes locally (ESLint + angular-eslint)
• bun run test passes locally (Vitest) — not applicable, workflow-only change
• bun run build passes locally (no type errors, no budget exceeded) — not applicable, workflow-only change
• New components use ChangeDetectionStrategy.OnPush and Angular signals — not applicable
• No localStorage/sessionStorage access for JWT tokens (use the auth store)
• No bypassSecurityTrust* calls without explicit review
• No secrets, credentials, or .env content committed
• CHANGELOG.md updated under [Unreleased] — not needed for a one-line CI fix

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How to Test

After the release to main, the "Deploy" workflow run in this repo triggers "Deploy MVP" in Kntro-Soft/reqsai-infra with web_ref=<sha> and api_ref=keep; the API container is not recreated.