fix: broaden llama.cpp grammar error classifier to match newer builds

[gonzalofrancoceballos]

Problem

The llama.cpp grammar error classifier in agent/error_classifier.py only recognizes older error phrasing ("error parsing grammar"), but newer llama.cpp builds return "Failed to initialize samplers: failed to parse grammar". When the classifier fails to match, Hermes skips the grammar recovery path (stripping pattern/format keywords from tool schemas and retrying locally) and falls directly to a cloud fallback provider.

This is especially impactful for users running local inference via custom providers (llama.cpp) with MCP servers whose tool schemas include regex patterns like "\\d{4}-\\d{2}-\\d{2}".

Reproduction

# Local llama.cpp server returns HTTP 400:
curl http://localhost:8080/v1/chat/completions -H "Content-Type: application/json" -d '{
  "model": "qwen3-80b-next-q4_k_m",
  "messages": [{"role":"user","content":"test"}],
  "tools": [{"type":"function","function":{"name":"f","parameters":{"type":"object","properties":{"d":{"type":"string","pattern":"\\d{4}-\\d{2}-\\d{2}"}}}}}],
  "max_tokens": 50
}'
# → {"error":{"message":"Failed to initialize samplers: failed to parse grammar"}}

In Hermes, this error passes through the classifier unrecognized, triggering cloud fallback instead of the schema-stripping recovery.

Fix

Added "failed to parse grammar" to the match list in the classifier condition, alongside the existing "error parsing grammar" and "unable to generate parser" checks.

Changes

• agent/error_classifier.py: Added "failed to parse grammar" in error_msg condition
• tests/agent/test_error_classifier.py: Added test_llama_cpp_failed_to_parse_grammar test case

Testing

pytest tests/agent/test_error_classifier.py::TestClassifyApiError::test_llama_cpp_failed_to_parse_grammar
# PASSED
pytest tests/agent/test_error_classifier.py::TestClassifyApiError::test_llama_cpp_grammar_parse_error
# PASSED (existing test still passes)