choose_cheap_model_route misses inflected keyword forms

Description

hermes-agent's `choose_cheap_model_route` keyword matching does not handle inflected word forms. The keyword list contains `'implement'` but not `'implementing'`, `'testing'` routes to the cheap model even though `'test'` was meant to use the expensive model.

Reproduction

# 'can you do some testing' → routed to cheap model
# 'implement' in keywords but 'implementing' is not
# Inflected forms bypass the intended routing logic