fix: make config set examples use placeholder syntax

[stablegenius49]

Summary

• replace literal KEY VALUE examples with <key> <value> placeholders in the setup summary and config CLI output
• update the config set usage text so copy-paste examples no longer write a literal KEY: VALUE entry into config
• add focused CLI output tests covering the setup summary and missing-args usage path

Testing

• /opt/homebrew/bin/python3.11 -m pytest -o addopts='' tests/hermes_cli/test_config.py tests/hermes_cli/test_set_config_value.py tests/hermes_cli/test_placeholder_usage.py -q

Closes #926

[teknium1]

Merged via PR #1322. Your substantive commit was cherry-picked onto current main with authorship preserved, with a small follow-up for the remaining fallback help text. Thanks for the fix.