- tracing.py: add compile_prompt() that uses Langfuse .compile(**vars)
for {{variable}} substitution, falls back to Python .format() for
hardcoded {variable} templates
- agent_runner.py: replace _get_system_prompt().format() with
tracing.compile_prompt() for batch_file_classifier, batch_processing,
batch_cloud_processing prompts
- journey.py: replace get_prompt + .format() with compile_prompt()
for journey_system prompt
- chat tracing.py: add compile_prompt() for parity (chat prompts
currently have no variables, but ready for future use)
- Remove unused _get_system_prompt helper
ccba54ac24