Un-wire the known-broken mass_update_stage bulk button until #508 lands #588

Follow-up scoping decision on #508, from the 2026-08-02 review.

Problem

mass_update_stage is documented KNOWN-BROKEN in its own source (src/actions/opportunity.actions.ts:661-670: "kept wired and tracked in issue #508. No invocation path currently executes it.") — yet it is still listed in bulkActions on the opportunity list view (src/views/opportunity.view.ts:77).

Net effect for a real user: the button renders, is clickable, and silently does nothing. That is worse than the button being absent — it reads as data loss / product breakage, not as a tracked platform gap.

Fix

• Remove mass_update_stage from the view's bulkActions array; keep the action definition in place with its tracking comment so the wiring is a one-line restore.
• Leave a pointer comment at the removal site referencing mass_update_stage is wired but cannot execute — every bulk-action invocation path is broken in console 16.1.0 #508, so the button returns in the same PR that verifies the console's bulk-invocation path works.

Acceptance

• Opportunity list view renders no dead bulk button.
• mass_update_stage is wired but cannot execute — every bulk-action invocation path is broken in console 16.1.0 #508 remains the tracking issue for the underlying invocation-path breakage; this issue only covers the UX of not shipping a dead control.