Lexicon checker: cross-topic duplicate reports and element label cleanup

_build/lexicon/README.md

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+# Core lexicon checker
+
+Tooling for [issue #14512](https://github.com/modxcms/revolution/issues/14512).
+
+## Run
+
+Requires `_build/build.config.php` and `_build/build.properties.php` (see the sample files).
+
+```bash
+php _build/lexicon/checklexicon.php [language] [excludedFolders]
+```
+
+Default language is `en`.
+
+## Reports
+
+Generated files are gitignored (`_*.php` in this folder):
+
+| File | Meaning |
+|------|---------|
+| `_missing.php` | Keys referenced in core but not defined |
+| `_superfluous.php` | Keys defined but not found by static scan |
+| `_variable.php` | Dynamic / concatenated key usage |
+| `_duplicates_identical.php` | Same key + same value in multiple **core** topics |
+| `_duplicates_conflict.php` | Same key with **different** values across **core** topics |
+
+Cross-topic duplicate reports cover `core/lexicon/{lang}/` only. Setup language files are still scanned for missing/superfluous usage checks.
+
+## Safety notes
+
+- `_superfluous.php` is a **candidate list**, not an automatic delete list. Extras may call core lexicon keys that the scanner never sees.
+- Prefer removing **identical** cross-topic duplicates first (keep the copy in `default` when the manager always loads that topic).
+- Resolve `_duplicates_conflict.php` carefully: conflicting values usually mean a key is overloaded and should be renamed, not deleted.
+- The CLI exits `0` after writing reports; use the report files (especially `_duplicates_conflict.php`) for review gates.