feat(health-check): default the ALB health route to Laravel's /up

[stevethomas]

Hey, I made a thing! 🥳

Great! Now please answer the following questions to help out your assigned reviewer:

What problems are you solving?

• The ALB target-group health check defaulted to /health, a route every app had to hand-roll. Flipping the default to /up — Laravel's built-in health route (11+) — means a stock Laravel app is health-checkable out of the box.
• /up boots the full framework and returns 200 only on a clean boot (500 otherwise), so it still satisfies YOLO's "exercise PHP so a broken boot fails the check" requirement — no static Caddy 200 that would mask a broken boot.

Is there anything the reviewer needs to know to deploy this?

• The path stays overridable per app via tasks.web.health-check.path — only the default changed.
• TargetGroup implements SynchronisesConfiguration, so this reaches live target groups on the next yolo sync — it'll ModifyTargetGroup any existing group still on /health over to /up. An already-deployed app that defines /health but not /up would start failing health checks after a sync. Stock Laravel apps (CL included) already ship /up, so no impact there — just eyeball any older app that predates the /up route before syncing it.

Changes

• TargetGroup::reconcilableHealthCheck() default /health → /up (+ rationale comment).
• Tests: default fixtures → /up; the override test now sets /health so it still proves the manifest override bites.
• Docs: manifest reference (example + table + prose) and the images/container-contract guide updated, with the prose now explaining the /up boot behaviour and the DiagnosingHealth event, linked to Laravel's health-route docs.

Verification

• 553 Pest passing · pint clean · phpstan clean · VitePress build clean (no dead links).

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