feat(offset): open on the live preview for pre-selected objects; signed typed distance

With objects already selected, OFFSET opens at the side step with the
preview following the cursor instead of asking for a distance first
(#422). At the side step a typed distance places the offset at once on
the cursor's side, and a negative one on the other side; Enter at the
start repeats the last distance (#418). Erase and Layer, which lived on
the skipped distance step, are offered there too. With nothing selected
the distance-first flow is unchanged.

The opposite side is found by mirroring the cursor through its nearest
point on the outline, capped at half the offset distance so it cannot
cross a narrow gap back to the cursor's own side. Two new prompts are
added to the catalog and every locale.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/locale_catalog.rs

@@ -2049,6 +2049,8 @@ pub(super) fn message_attribute(source: &str) -> Option<(&'static str, &'static
         "OFFSET%{n}  Click through point or [Multiple]:" => Some(("modify", "offset-n-click-through-point-or-multiple")),
         "OFFSET%{n} Multiple  Click next side [distance %{d}]:" => Some(("modify", "offset-n-multiple-click-next-side-distance-d")),
         "OFFSET%{n} Multiple  Click next through point:" => Some(("modify", "offset-n-multiple-click-next-through-point")),
+        "OFFSET%{n}  Click through point or type distance, negative for the other side [Multiple/Erase/Layer] <%{d}>:" => Some(("modify", "offset-n-click-through-point-or-type-distance")),
+        "OFFSET%{n} Multiple  Click through point or type distance, negative for the other side [Erase/Layer] <%{d}>:" => Some(("modify", "offset-n-multiple-click-through-point-or-type-distance")),
         "OK" => Some(("common", "ok")),
         "OLE Frame" => Some(("properties", "ole-frame")),
         "OOPS: nothing to restore." => Some(("file", "oops-nothing-to-restore")),