fix(portal): mark disabled Jobs board as setup required

[gossion]

Summary

• return a distinct setup_required state when the computed Jobs board has no configured scope
• render a setup guide instead of an outage-style error for that expected state
• preserve existing error handling for Kubernetes access and query failures

Validation

• cd portal; go test ./internal/portalapi -run 'TestConfiguredJobsModesAllowMissingKubernetesReader|TestPortalShellContainsWorkspaceScopeContract' -count=1 -v
• python3 scripts/check-license-headers.py

[Copilot]

Pull request overview

This PR updates the Portal “Jobs” computed board to distinguish an expected “not configured yet” condition from genuine outages by returning a dedicated setup_required state when no Jobs scope mode is configured, and rendering a setup guide in the UI for that state. This keeps the existing behavior for real Kubernetes access / query failures.

Changes:

• Return state: "setup_required" (with a setup-oriented reason) when Jobs scope mode is disabled/unset.
• Extend the frontend fetchJSON error handling to preserve status and state from scoped JSON error envelopes.
• Render a “Jobs board setup required” guide (instead of an outage-style warning) when receiving the setup_required state; update tests accordingly.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
portal/internal/portalapi/server.go	Emits a setup_required state for the disabled Jobs board gate via writeScopedJSON.
portal/internal/portalapi/server_test.go	Updates expectations to assert the new reason text and that the disabled response includes "state":"setup_required", and verifies the portal shell contains the new UI contract strings.
portal/internal/portalapi/assets/index.html	Propagates status/state on thrown fetch errors and renders a setup guide for 503 + setup_required.

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[Pengfei Ni (feiskyer)]

LGTM