feat(dates): print the numeric offset in the audit report

The spec-mirroring review noted the report showed the offset SOURCE
but not the offset value — the value is what the operator spot-checks.
Each proposed line now ends with offset={+N}m (or - for utc_direct
rows). Tests pin the rendered values.

src/filename_audit.rs

@@ -267,8 +267,16 @@ pub fn format_report(rows: &[AuditRow], skipped: &[SkippedLibrary]) -> String {
             .tz_source
             .map(|t| t.as_str().to_string())
             .unwrap_or_else(|| "-".into());
+        // The numeric offset (minutes ahead of UTC) is the value the
+        // operator actually spot-checks: a wall pattern resolved with
+        // empty evidence carries the server zone's offset for that date.
+        let proposed_offset = row
+            .proposed
+            .camera_offset_minutes
+            .map(|m| format!("{m:+}m"))
+            .unwrap_or_else(|| "-".into());
         out.push_str(&format!(
-            "{}\t{:<19}\t{:<20}\tlib={} {}\n  current:  {}\n  proposed: {} [{}] tz_source={}\n",
+            "{}\t{:<19}\t{:<20}\tlib={} {}\n  current:  {}\n  proposed: {} [{}] tz_source={} offset={}\n",
             if row.changed { "*" } else { " " },
             row.pattern,
             row.rel_path,
@@ -278,6 +286,7 @@ pub fn format_report(rows: &[AuditRow], skipped: &[SkippedLibrary]) -> String {
             format_epoch_utc(Some(row.proposed.timestamp)),
             row.proposed.source.as_str(),
             proposed_tz,
+            proposed_offset,
         ));
     }
     if !skipped.is_empty() {
@@ -434,6 +443,8 @@ mod tests {
             inv.proposed.tz_source.map(|t| t.as_str()),
             Some("assumed_server")
         );
+        // Server zone America/New_York is EDT (UTC-4) in June.
+        assert_eq!(inv.proposed.camera_offset_minutes, Some(-240));
         assert!(inv.changed, "stored exif date must flag as changed");
 
         // The unix timestamp: utc_direct, no offset, and the stored row
@@ -544,6 +555,10 @@ mod tests {
         assert!(first.contains("*\t"), "changed row must be flagged");
         assert!(first.contains("screenshot"));
         assert!(first.contains("utc_direct"));
+        // Numeric offset is printed: the wall row carries the server-zone
+        // offset for that date, timestamp rows have none.
+        assert!(first.contains("offset=-240m"));
+        assert!(first.contains("offset=-\n"));
         // The stored source renders without debug quotes (P1 from
         // review): `2021-... [exif]`, never `["exif"]`.
         assert!(first.contains("[exif]"));