v0.5.1 — capability wording

Wording follow-up to v0.5.0 (the per-stack capability guard).

• The target_type tool description now also notes that supported object types can differ between on-premise / private cloud systems depending on the system version (not only between cloud and on-prem).
• Removed speculative "future per-release class (zcl_i18n_service_2022 / _2025)" wording from the tool description, i18n-client, abap/README, and both ABAP handlers.

No behaviour change; capability guard still degrades to permissive until the ABAP capabilities action is imported.

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