[UI] Destructive action confirmation dialogs and discard-changes guards (Phase 11)

[CRamsan]

Phase 11 — Destructive Action Guards

Implement confirmation dialogs for all destructive actions and discard-changes guards on all form screens. This is split from #410 which covered the entire MVP Polish epic.

POL-05: Confirmation Dialogs for Destructive Actions

Define a reusable ConfirmationDialog composable:

@Composable
fun ConfirmationDialog(
    title: String,
    body: String,
    confirmLabel: String,
    onConfirm: () -> Unit,
    onDismiss: () -> Unit,
    isDestructive: Boolean = true,
)

When isDestructive = true, confirm button uses MaterialTheme.colorScheme.error.

Apply to: Delete Unit, Delete Task, Remove Occupant, Cancel Invite, Leave Organization.

ViewModel pattern: manage pendingDestructiveAction: DestructiveAction? field — non-null triggers dialog; on confirm executes then clears; on dismiss clears without executing.

POL-06: Discard Changes Guard

All form screens must warn before losing unsaved changes.

Form screens requiring this guard: AddEditUnitScreen, AddEditTaskScreen, AddOccupantScreen, EditProfileScreen, AddPaymentRecordScreen, SubmitRequestScreen.

Implementation:

• Each form ViewModel exposes isModified: Boolean in UIState — set to true when any field changes from its original value
• BackHandler(enabled = viewModel.isModified) intercepts back navigation
• Dialog: title "Discard unsaved changes?", body "Your changes will be lost.", Discard (destructive) / Keep Editing (neutral)
• Top bar back arrow must also trigger this guard (not bypass it)

Dependencies

• All feature screens listed above must exist before guards can be applied
• [POLISH] Empty states, loading states, and confirmation dialogs across all screens (Phase 11) #410 — Accessibility and UI states (sister polish issue)

What type of task is this?

Development