gemma-4 GGUF finetunes don't emit a clean EOS after a tool call — they continue
and hallucinate a fake tool result (<tool_call|><|tool_response>response:NAME{…}
… <turn|>), wasting tokens on a result llama.cpp never runs. Add a per-model stop
augmentation (_augment_model_stops): for gemma, inject <|tool_response>,
<tool_response|>, <turn|> and the real <end_of_turn> as stop strings (merged with
any client-supplied stops). llama.cpp matches and trims stop strings, so the call
ends cleanly and the fake-response tail is never generated. Applied to both chat
methods and the raw completion paths; non-gemma models are unaffected.

Complements 5135f8f8 (parser repair of <|"|> quotes and malformed markers).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011DDv7BchtZQWsnPG6Jm49m