* Add get_json_string_field helper
Introduce get_json_string_field in OrcaCloudServiceAgent.cpp to safely extract string fields from JSON objects.
* Add resolve_display_name helper
Introduce resolve_display_name to normalize provider metadata labels for the UI. The helper returns the first non-empty value from display_name, nickname, full_name, name, falling back to username, resolving human-facing label across varying provider payloads.
* Replace safe_str anonymous function
Replace get_json_string_field for better readability.
* Replace resolution flow for nickname with function
Consolidate both flows into one function for easier maintenance and more consistency.
* Update OrcaCloudServiceAgent.hpp
* Add OrcaCloudServiceAgent display name tests
Add unit tests verifying OrcaCloudServiceAgent resolves a user's display name from various session JSON shapes.
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