chore(i18n): stop tracking generated locale/*.po copies

az.po/ru.po under invoice_az/locale are regenerated (overwritten) by the
az_locale app on every `bench migrate` via setup_locale. Tracking them meant
every migrate dirtied the tree and blocked `git pull`
("local changes would be overwritten by merge").

Untrack them and gitignore locale/*.po so migrate can regenerate freely and
pull stays clean. Masters remain the source of truth in the az_locale repo;
main.pot (extraction template) stays tracked.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.gitignore

@@ -56,3 +56,9 @@ jspm_packages/
 
 # HAR captures (may contain Bearer tokens / PII)
 *.har
+
+# Per-app translation copies (az.po/ru.po) are generated and overwritten by the
+# az_locale app on every `bench migrate` (setup_locale). Masters live in the
+# az_locale repo, so keeping these tracked only dirties the tree and blocks
+# `git pull`. Untrack them; main.pot (the extraction template) stays tracked.
+invoice_az/locale/*.po