feat(isce2): harden managed production flow

- add one-time base DEM preparation utility and prepared-first DEM resolution

- support geocode resume/full-geocode and guard large unprepared DEMs

- repair missing completion files during in-place ISCE2 publish rebuild

- add ISCE2 stabilization update log

backend/app/isce2_pipeline/lt1_input_resolver.py

@@ -250,4 +250,4 @@ def _prepared_dem_variants(value: str | Path) -> tuple[str | Path, ...]:
         return ()
     if text.lower().endswith(".wgs84"):
         return (value,)
-    return (value, f"{text}.wgs84")
+    return (f"{text}.wgs84", value)