Fix customer transaction heading reusing lang_Addexpensing key

[Tyagiquamar]

Issue #446: the customer transaction heading reused lang_Addexpensing, which is meant to read "Customer" on the customer screen but collided with the expense modal's "Add" meaning. Switch the customer heading to the existing lang_customer_title key. i18n coverage stays clean (exit 0).

[github-actions]

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[sridharkalaibala]

Thanks for fixing this heading. I checked the one-line diff and reproduced the two desktop i18n failures locally with node --test tests/i18n.test.js (49 passed, 2 failed). The existing lang_customer_title means plural Customers, while this heading says singular Customer, so reusing it still violates the one-key/one-meaning rule. Please use a singular customer key with matching meaning (or add a dedicated key), update the English inventory with node tests/tools/i18n-coverage.js --write-english, and rerun the full i18n suite. The inventory also retains the now-unused lang_Addexpensing key. git diff --check passed. The CLA check is still pending your signature as described by the bot. Once these checks are green, this focused correction can be reconsidered.