ADR-0070 D5 tail: retire the "Local / Custom" stopgap scope from the Studio selector (once envs are orphan-free)

[xuyushun441-sys]

Final step of ADR-0070 D5 (migration), split out of Epic #2278 because it is gated on a runtime precondition, not just code.

Context

The "Local / Custom (this env)" package-selector scope (objectui#1946) was a stopgap that surfaced the package-less (package_id = null) orphan bucket. ADR-0070 repurposes it as a migration affordance and says it should be removed "once an environment has no orphans."

The migration tooling that makes removal safe is already merged:

• kernel: protocol.reassignOrphanedMetadata + POST /packages/:id/adopt-orphans (framework#2301)
• Studio UI: the "Adopt loose items" action in PackagesPage.tsx (objectui#1983)
• new orphans are prevented at the kernel by writable_package_required (framework#2285)

So all that remains is removing the scope itself once it is empty.

Still present (to remove)

../objectui/packages/app-shell/src:

• layout/ContextSelectors.tsx — the "Local / Custom (this env)" / 本地 / 自定义（本环境） option
• views/metadata-admin/package-scope.ts — isLocalScope() + the sentinel scope helpers

Acceptance

• A guard/telemetry confirms target envs report 0 orphans (reassignOrphanedMetadata would reassign nothing), OR the scope is shown only while orphans exist (auto-hide when empty).
• Remove the "Local / Custom" scope from the selector; drop isLocalScope and the null/sys_metadata create-destination path.
• ADR-0070 D5 §"retire the stopgaps" can be ticked.

Out of scope

The kernel null-as-legacy-overlay read path stays (ADR-0070 D5: null survives as a read-side rehydration tag for legacy rows).

Repo: ../objectui. Parent epic: #2278.

[os-zhuang]

Implemented in objectui#2025 — pre-launch, so removed outright (no env migration needed). Removes the "Local / Custom" selector scope + isLocalScope/LOCAL_PACKAGE_ID; create-flow and list/home filters now always resolve a real writable base. Read-side sys_metadata legacy-provenance handling kept per ADR-0070 D5. Closes when that PR merges.