- 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
- _get_system_prompt helper: fetches managed prompts from Langfuse
with hardcoded fallback (same pattern as chat service)
- journey.py: journey_system prompt manageable via Langfuse
- agent_runner.py: batch_file_classifier, batch_processing,
batch_cloud_processing prompts all manageable via Langfuse
- redis_consumer.py: link_prompt_to_trace for all three handlers
