fix(ci): split smoke gate — required curl smoke + advisory Playwright

[agjs]

Problem

The combined smoke gate was the chronic CI pain point:

• Boots compose + runs the full Playwright Chromium suite in one job.
• 20-min timeout — slow signal on legitimate failures.
• Playwright surface (browser timing, animation, transient network) flakes occasionally; flake = blocked PR until rerun.
• Sometimes the runner gets stuck pre-start and GitHub's job timeout doesn't apply; the run hangs indefinitely until manually cancelled. Happened today on run `26681455502`.

Change

Split into two workflows so each part has the cost/value contract that suits it:

Workflow	Required?	What it does	Timeout
`infra-compose-full-stack-smoke.yml`	✅ required	curl-only register → login → /me → register-new → dashboard round-trip	8 min (was 20)
`infra-compose-playwright-e2e.yml`	❌ advisory	boots same stack, runs apps/ui Playwright Chromium suite	15 min

The curl smoke completes in ~3–4 min on warm runners; the 8-min ceiling fails fast instead of hanging for 20. Playwright failures stop being merge blockers — a flake means "go look at the run", not "rerun and hope".

Also drops the OpenAPI schema check that was bundled into smoke — `apps-api-openapi-drift.yml` already runs the same check as a dedicated required workflow.

Operator follow-up

The Playwright job name `UI Playwright E2E (browser-based smoke)` will appear in the required-check picker once it runs once. Leave it OFF — that's the whole point of the split.

Test plan

• Both YAMLs parse / yaml-lint clean
• Pre-push smoke gate green
• This PR self-verifies: smoke gate runs in curl-only mode + Playwright runs as advisory. If smoke is fast and green and Playwright either passes or fails-without-blocking, the split works.