Connect new ALBs to workloads, and stop pools pointing at one workload

[mattdjenkinson]

Problem

• An ALB with several backends still showed a "View workload" chip. It linked to whichever workload published the ALB, which is only one backend in the pool.
• The "No backend available" headline came from the same label. Deleting that one workload would have reported the whole pool as down, even with other backends still serving.
• You could only point a new ALB at a public origin, even in projects with compute.

Solution

Pools on the overview

• The health strip no longer speaks for a single workload when there's more than one backend. It shows the "N backends" chip that URL pools already use. Hovering it lists every backend with its share of traffic, or "No traffic" / "Deleted".
• Each workload row on the Backends card links to that workload's page.
• Workloads that were deleted while the pool still references them get a "Workload deleted" chip, and their link is dropped.
• The headline now judges a pool by its rows:
  • "1 of 3 backends unavailable", with a "Manage backends" chip, when some workloads are gone.
  • "No backend available" only when nothing that receives traffic is left.
  • Backends with weight 0 don't count.
• Single-backend ALBs behave as before.

Workload origins when creating an ALB

• In projects entitled to compute, Add an Application Load Balancer offers the same Public internet / Datum compute choice as Add backend. Projects without compute see the dialog as before.
• Compute availability comes from useComputePluginSlug, the same check the sidebar uses for Compute > Workloads.
• The new ALB's first backend is the workload's NetworkService and the chosen port.
• The ALB isn't given the compute workload-name label. That label means the workload's deploys manage the ALB, and that deleting the workload deletes it.
• The origin cards and workload/port selects moved to form/origin-type-fields.tsx, shared by both dialogs.
• Add backend now hides "Datum compute" in projects without compute. When you edit a backend that already points at a workload, the choice stays visible so you can still repoint it.

Dependency

• @datum-cloud/datum-ui goes from 3.4.0 to 3.4.1. The patch only lightens badge borders.

Test plan

• bun run typecheck, eslint, prettier
• bun test app: 1398 pass. New tests cover the per-row deleted-workload state, the create payload for a workload origin, and schema validation for each origin type.
• Checked locally: create dialog with Datum compute, and the backend tooltip on a 3-backend pool (screenshots above)
• Create an ALB from a workload and confirm it serves traffic
• Delete one workload in a pool and check the headline and row chip

[github-actions]

🧪 Test Summary

Job	Status
Bun Unit Tests	✅ success
E2E Regression (0)	✅ success
E2E Regression (1)	✅ success
E2E Regression (2)	✅ success
E2E Regression (3)	✅ success
E2E Smoke	✅ success
Unit Tests	✅ success

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