refactor: rename soft-delete marker from .deleted to .closed

Internal rename: DELETE_MARKER -> CLOSE_MARKER, DeleteMarker ->
CloseMarker, is_deleted -> is_closed. The batch UUID is dropped;
undo now groups cases by their exact closed_at timestamp, which
bulk-close writes identically across its selection while per-case
close writes a unique stamp.

Behavior unchanged. No migration (project is pre-production);
legacy .deleted files in tmpdata were removed manually.

server/src/routes/bulk.rs

@@ -3,9 +3,8 @@ use std::sync::Arc;
 use axum::extract::State;
 use axum::response::Redirect;
 use axum_extra::extract::Form;
+use doctate_common::timestamp::now_rfc3339;
 use serde::Deserialize;
-use time::OffsetDateTime;
-use time::format_description::well_known::Rfc3339;
 use tracing::{info, warn};
 
 use crate::analyze::{ANALYSIS_INPUT_FILE, AnalyzeJob, AnalyzeSender, DOCUMENT_FILE};
@@ -13,7 +12,7 @@ use crate::auth::AuthenticatedWebUser;
 use crate::config::Config;
 use crate::error::AppError;
 use crate::events::{self, CaseEventKind, EventSender};
-use crate::paths::{DeleteMarker, write_delete_marker};
+use crate::paths::{CloseMarker, write_close_marker};
 use crate::routes::case_actions::{
     build_analysis_input, reset_case_artefacts, write_input_create_new,
 };
@@ -140,16 +139,9 @@ async fn bulk_delete(
     user_root: &std::path::Path,
     case_ids: &[String],
 ) {
-    // One batch UUID + one timestamp shared across the entire bulk action,
-    // so undo can restore exactly this group.
-    let batch = uuid::Uuid::new_v4();
-    let deleted_at = match OffsetDateTime::now_utc().format(&Rfc3339) {
-        Ok(s) => s,
-        Err(e) => {
-            warn!(slug = %slug, error = %e, "bulk-delete: failed to format timestamp");
-            return;
-        }
-    };
+    // Shared `closed_at` across the whole bulk action: identical timestamp
+    // groups the cases so a subsequent undo can restore exactly this click.
+    let closed_at = now_rfc3339();
     let mut ok = 0usize;
     let mut skipped = 0usize;
     for case_id in case_ids {
@@ -163,11 +155,10 @@ async fn bulk_delete(
             skipped += 1;
             continue;
         };
-        let marker = DeleteMarker {
-            batch,
-            deleted_at: deleted_at.clone(),
+        let marker = CloseMarker {
+            closed_at: closed_at.clone(),
         };
-        if let Err(e) = write_delete_marker(&case_dir, &marker).await {
+        if let Err(e) = write_close_marker(&case_dir, &marker).await {
             warn!(slug = %slug, case_id = %case_id, error = %e, "bulk-delete: write marker failed");
             skipped += 1;
             continue;
@@ -175,7 +166,7 @@ async fn bulk_delete(
         events::emit(events_tx, slug, case_id, CaseEventKind::CaseDeleted);
         ok += 1;
     }
-    info!(slug = %slug, batch = %batch, ok, skipped, "bulk-delete completed");
+    info!(slug = %slug, closed_at = %closed_at, ok, skipped, "bulk-delete completed");
 }
 
 async fn bulk_reset(