fix(cli): mark sessions command as cli_only

[AllynSheep]

Summary

The /sessions slash command is registered in COMMAND_REGISTRY but has no handler in either the gateway dispatcher or the CLI dispatcher. It results in a silent no-op — the user sends /sessions and gets zero response.

Fix

Mark sessions as cli_only=True so it is excluded from GATEWAY_KNOWN_COMMANDS. The interactive session browser requires keyboard navigation and is not feasible in messaging gateways.

Changes

• hermes_cli/commands.py: Added cli_only=True to sessions command definition

Testing

• hermes sessions browse continues to work in CLI mode
• Gateway now properly rejects /sessions with unknown command handling

Closes #23533

[alt-glitch]

Duplicate of #22962 — both wire up /sessions handling. #22962 adds dispatch branches in process_command(); this PR marks sessions as cli_only to exclude from gateway.

[teknium1]

Thanks for identifying the original /sessions no-op and for the duplicate discussion pointing to the dispatch-based fix.

Automated hermes-sweeper review found that current main now implements the requested behavior more completely:

• Classic CLI dispatches /sessions in cli.py:8627 and handles listing/resume in hermes_cli/cli_commands_mixin.py:827 (introduced by d6c488f2dce96a1d1375c8e7e089b54a1e7ae6f4).
• Gateway dispatches /sessions in gateway/run.py:9901; gateway/slash_commands.py:3693 provides a scoped session listing/resume handler (introduced by 3e7e9b24d40c6ff62e50936ba8b8184ad61da322, shipped in v2026.6.19).
• tests/gateway/test_resume_command.py:780 verifies gateway dispatch, and the command is documented as available on both CLI and messaging gateways at website/docs/reference/slash-commands.md:257.

Marking the command CLI-only would now suppress that supported gateway behavior, so this PR is superseded by main.