refactor(dashboard-api): remove legacy team mutations

[ben-fornefeld]

Summary

• remove the nine superseded legacy team and admin-user mutation routes
• remove their OpenAPI contract, generated handlers, transition gate, feature flag, provisioning graph, tests, and documentation
• retain /v1/management, generic JWT verification, projected identities, and Ory-backed profile/member reads

Validation

• cd packages/dashboard-api && make generate && go test ./... -run '^$'
• focused management readiness, identity, identity-profile handler, API, middleware, and feature-flag tests
• git diff --check
• Full database-backed tests require Docker/Testcontainers; the local Docker daemon was unavailable.

Sponsor: @ben-fornefeld

[cursor]

PR Summary

Medium Risk
Breaking removal of team/user lifecycle and billing-provision endpoints from dashboard-api; incorrect or lagging client migrations could block signups, team changes, or admin workflows until callers use the workspace API.

Overview
This PR removes the legacy dashboard-api write surface for teams, members, admin user bootstrap/delete, and admin cluster assign/detach, along with the OpenAPI contract, generated routes, LaunchDarkly 412 gate, billing team-provision sink, and the internal provisioning stack that backed those flows.

Reads and admin controls stay: listing teams, members, limits, template/build routes, ban/block, cluster GET, and /v1/management (including project cluster assign/detach via the shared assignTeamCluster / detachTeamCluster helpers). Docs now describe dashboard-api as read-oriented plus management projection rather than legacy provisioning.

Any client still calling the deleted REST mutations must move to the workspace API; signup and team creation are no longer handled here.

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