[API] Restore public CLI handler compatibility imports

[podkidyshev]

Summary

• Restore public cloudai.cli.handlers imports as deprecated forwarding wrappers after the handler-module rename in [API] Move shared handlers out of the CLI package #1046.
• Preserve each function's arguments, return value, and exceptions. Calls emit a DeprecationWarning at the caller.

Test Plan

• Automated CI.
• Manual local Python check: a legacy public handler listed registered agents and emitted one caller-facing deprecation warning.

Additional Notes

This PR changes only the compatibility module. Follow-ups: #1063 (CLI config/listing), #1064 (CLI execution), #1060 (Path API), #1061 (TOML text), and #1062 (background execution).

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