Fix: Guard quick_commands against non-dict values

Problem

When quick_commands values in ~/.hermes/config.yaml are not dicts (e.g., strings like foo: ''), the slash command dispatch at cli.py:6583 crashes with:

Error: 'str' object has no attribute 'get'

This blocks all matching slash commands — even valid skill commands — because quick_commands is checked before the skill dispatch chain.

Reproduction

# ~/.hermes/config.yaml
quick_commands:
  foo: ''

Then type /foo — crash.

Fix

Add isinstance(qcmd, dict) guard before accessing .get(). Non-dict entries now get a warning log and fall through to plugin/skill command checks instead of crashing.

Fixes #18816