Move concretize-defaults changelog entries to In progress

Signed-off-by: Hugh Carson <hughcars@amazon.com>

Author: hughcars

CHANGELOG.md

@@ -23,6 +23,16 @@ The format of this changelog is based on
   - Enabled voltage and impedance postprocessing for waveport and BoundaryMode by specifying a line
     from ground to conductor, either through mesh coordinates or boundary attribute
     in `config["Boundaries"]["Postprocessing"]["Impedance"]` [PR 657](https://github.com/awslabs/palace/pull/657).
+  - Palace now writes a fully-resolved copy of the run configuration to
+    `<output_dir>/config.json` at startup, with every implicit default and `"Default"`
+    sentinel filled in. The sidecar passes schema validation and can be used to re-run
+    the same simulation deterministically [PR 719](https://github.com/awslabs/palace/pull/719).
+
+#### Interface Changes
+
+  - `Solver.Eigenmode.MaxSize` now defaults to `max(2 * N, N + 15)` for both SLEPc and
+    ARPACK. `Solver.Eigenmode.MaxIts` now defaults to `1'000'000`
+    [PR 719](https://github.com/awslabs/palace/pull/719).
 
 #### Bug Fixes
 
@@ -76,11 +86,6 @@ The format of this changelog is based on
     ([mfem/mfem#5246](https://github.com/mfem/mfem/pull/5246))
     [PR 706](https://github.com/awslabs/palace/pull/706).
 
-#### Interface Changes
-
-  - `Solver.Eigenmode.MaxSize` now defaults to `max(2 * N, N + 15)` for both SLEPc and
-    ARPACK. `Solver.Eigenmode.MaxIts` now defaults to `1'000'000` [PR TBD].
-
 ## [0.16.0] - 2026-03-05
 
 #### New Features