Refactor: Extract observability into dedicated module

- Created ObservabilityManager class encapsulating all Langfuse/OTEL logic
- Methods: initialize(), track_generation(), track_tool_use(),
  track_tool_result(), track_session_totals(), finalize(), cleanup_on_error()
- All security features preserved (URL validation, secret sanitization, timeouts)
- Maintains state for both Langfuse and OTEL platforms

Replaced ~350 lines of scattered observability code with clean manager calls

Signed-off-by: sallyom <somalley@redhat.com>

Author: sallyom