UX: Slash commands require exact full name — partial matching and Tab completion not surfacing

[yxssxn]

Summary

Slash commands must be typed in full to register. Partial command entry (e.g. /con for /config, /mod for /model) returns "Unknown command" even when there is only one possible match.

Current behaviour

```
/con
Unknown command: /con
```

Expected behaviour

Either:

• Partial matching at execution time — if the prefix uniquely identifies one command, execute it (as Claude Code does)
• Tab completion surfaces reliably — the SlashCommandCompleter with complete_while_typing=True exists in the code but the completion dropdown does not appear consistently in CLI sessions

Technical context

SlashCommandCompleter is implemented in hermes_cli/commands.py and wired to the TextArea in cli.py with complete_while_typing=True. The completer correctly yields prefix-matched completions. The gap is at command dispatch time — the command handler does not attempt prefix matching, only exact matching.

A simple fix would be to check for unambiguous prefix matches in the command dispatcher before returning "Unknown command".

Environment

• Hermes Agent v1.0.0
• macOS 15.3
• CLI mode