Use canonical locations for compute placement

[scotwells]

What changed

• make projected Location names the canonical workload placement API
• route deployments and cells with topology.datum.net/location
• add --location across the compute CLI and show LOCATION in output
• keep --city as a deploy-time resolver with explicit ambiguity handling
• align portal views, samples, generated API docs, and e2e fixtures

Product impact

Users now choose the same locations exposed by datumctl get locations. City codes remain a discovery convenience, but generated workload configuration always records stable location names.

This intentionally breaks the alpha API: placements[].cityCodes becomes placements[].locations, and WorkloadDeployment.spec.cityCode becomes spec.locationRef. No migration compatibility is included.

Validation

• make test
• consumer UI tsc --noEmit
• provider UI tsc --noEmit