feat(dashboard-api): management route for the projected billing profile

[michalsuba-e2b]

Receiving side of EN-3221: teams born on global billing have no billing state on their control plane, which breaks regional readers (EN-3220 — bot-detection drops them entirely; the LaunchDarkly tier context and tier labels read a base_v1 that never updates). This adds the plane-side endpoint and tables the global plane pushes the profile into; the belt sender is https://github.com/e2b-dev/belt/pull/4397.

Current state:

• PUT /v1/management/projects/{projectID}/billing-profile (AdminJWTAuth), body {revision, has_payment_method, enterprise, plan?, decided_at?} — exact ManagementUpsertProjectLimits semantics: ledger-fenced (projection.billing_profiles), values written in the same transaction (public.team_billing_profiles), stale deliveries answered 204, team cache invalidated after commit (failed eviction logged, not returned — the limits convention).
• Migration adds the ledger + public.team_billing_profiles (has_payment_method, enterprise, plan nullable — a team without a row is unknown, never defaulted). No touch of project_limits, team_limits, or the auth path. By the mirroring convention the canonical copies of the migration and spec change live in belt go/oss/...; the belt PR carries them — whichever lands second is a no-op diff.
• Tests: write/advance, stale-revision drop (duplicate + older), invalid/missing project, committed-write-despite-failed-cache-eviction — against the real test DB, 4/4 green locally.
• Spec/sqlc regenerated (make generate in packages/db and packages/dashboard-api); api.gen.go churn is the generator's.

Draft until the belt sender PR is up and the contract has a billing-owner nod.

Sponsor: @michalsuba-e2b

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