[FEATURE] Leave Organization flow with sole-owner validation block

[CRamsan]

Status

Built, and appears to match requirements. This issue is mainly a verification/close-out pass, not new implementation,
unless the checks below turn up a real gap.

What's there

Implemented as an in-screen confirmation dialog on OrgDetailScreen (OrgDetailDialogState.ConfirmLeave), not a
separate screen — this matches edifikana/mockups/organization-detail.html, whose leave confirmation is an inline
modal, not a dedicated route.

• UI: OrgDetailContent's LeaveButton is disabled when uiState.isSoleOwner, with caption "Transfer ownership
  before leaving" (OrgDetailScreen.kt).
• Sole-owner detection: computed client-side in OrgDetailViewModel.initialize() from the member list
  (ownerCount == 1 && myMembership.role == OWNER).
• Confirm flow: confirmLeaveOrganization() calls MembershipManager.leaveOrganization(orgId), navigates to
  SettingsDestination.MyOrganizationsDestination (clearing the back stack) on success, shows a snackbar on failure.
• Backend independently enforces the same rule server-side (defense in depth, not just a client check):
  MembershipService.leaveOrganization() throws if isSoleOwner(orgId, callerId)
  (edifikana/back-end/.../service/MembershipService.kt).

Verification pass

• Confirm OrgDetailViewModelTest covers: sole-owner disables the button, non-sole-owner leave success path,
  leave API failure path
• Known gap to check: confirmLeaveOrganization() currently always navigates to MyOrganizationsDestination
  on success, regardless of how many organizations remain. Decide whether a user with zero remaining
  organizations after leaving should instead land on a Create/Join Organization flow — and check whether
  MyOrganizationsScreen even has an empty-state UI today (a scan of MyOrganizationsScreen.kt found none).
• If the above check out, close as complete; otherwise file the specific gap as its own scoped fix

Files

• edifikana/front-end/app/src/commonMain/.../features/settings/organizations/orgdetail/{OrgDetailScreen,OrgDetailViewModel,OrgDetailUIState}.kt
• edifikana/front-end/app/src/commonMain/.../features/settings/organizations/myorganizations/MyOrganizationsScreen.kt
• edifikana/back-end/src/main/kotlin/com/cramsan/edifikana/server/service/MembershipService.kt

Related

Parent: #392.