Added changelog

CHANGELOG.md

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+# Changelog
+
+## 1.4.0 - 2026-08-27
+
+Publication release of TRIMSP-NL Workbench corresponding to the modernization
+and validation described in the accompanying manuscript.
+
+### Added
+
+- Generalized target handling for layers containing more than five elements.
+- Runtime-selectable RANLUX, PCG32, and xoshiro256** random-number backends.
+- Explicit release, debug, profiling, and static Fortran build modes.
+- Standalone packaging support while retaining the browser-based workflow.
+- A named software version in the Fortran output.
+
+### Changed
+
+- Refactored the legacy Fortran source incrementally, including extraction of
+  GUI input handling and output-writing routines from the main transport flow.
+- Improved comments, variable documentation, and use of named constants.
+- Retained RANLUX as the default backend and preserved the established input-deck
+  format for backward compatibility.
+
+### Fixed
+
+- Corrected localized depth-bin index handling.
+- Corrected transmitted-energy accumulation.
+- Explicitly initialized recoil counters.
+- Corrected selected layer-index updates.
+
+### Validation
+
+The publication test suite contains 13 representative target configurations and
+143 energy-configuration points. The alternative RNG backends were compared with
+the historical RANLUX reference over 429 simulations in total. In that suite,
+the fast backends reduced the summed runtime by approximately a factor of two
+without a systematic backend-dependent trend in the reported implantation,
+backscattering, transmission, range, straggling, or representative profile
+observables.