Rollout gating and staging-to-production promotion

[seanmalbert]

• General
• Backend
• Public
• Partners

Background / Issue

Rollout is staged behind the per-jurisdiction enableDbDrivenContent flag, and admin-authored
changes are promoted between environments through the editor rather than direct DB sync.

Technical Context

• TDD: §7.2, §7.3.
• Wire enableDbDrivenContent end-to-end: UI visibility (Partners) and API enforcement share the
  flag; with it off, the public render path uses the existing static-import path. Add Export/Import
  actions to the editors (download the current screen's JSON; import PUTs it, reusing the editor's
  conflict resolution).
• Depends on: Translation admin CRUD (per-key) #6510; JurisdictionContent service and admin CRUD #6511; Partners translation editor #6516; Partners structured-content editor #6517

Acceptance Criteria

• With the flag off, the static-import render path remains active and the editors are hidden for
  jurisdictionAdmin; flipping it on switches the jurisdiction to DB-driven content.
• Export downloads the current screen's JSON; Import PUTs it in the target environment and surfaces
  the same conflict resolution as the editor on a since-changed target.
• Rollback (flag off) restores static rendering.

QA Notes

Public + Partners. Toggle the flag and confirm the public site and editor visibility switch
accordingly; export from staging and import to a target, including the conflict path when the target
changed after export. Confirm rollback restores static rendering.