feat: hot-reload pipeline files alongside rules

[mostafa]

Summary

• Store pipeline file paths in RuntimeEngine so that load_rules() re-reads pipeline YAML from disk before rebuilding the engine, instead of carrying over stale in-memory pipelines.
• Extend the notify file watcher to also watch individual pipeline files (in addition to the rules directory). Any YAML change triggers the same debounced reload signal.
• If any pipeline file fails to parse during reload, the entire reload aborts and the old engine stays active (same fail-safe pattern as rule reload errors).

Changes

File	What
rsigma-runtime/src/engine.rs	pipeline_paths field, set_pipeline_paths(), pipeline_paths(), reload_pipelines() helper
rsigma-runtime/src/processor.rs	reload_rules() carries pipeline_paths through to the new engine; 2 new tests
rsigma-cli/src/daemon/reload.rs	spawn_file_watcher() accepts and watches additional pipeline file paths
rsigma-cli/src/daemon/server.rs	DaemonConfig.pipeline_paths, engine setup, watcher setup, updated log messages
rsigma-cli/src/main.rs	Pass pipeline_paths into DaemonConfig

Test plan

• reload_re_reads_pipelines_from_disk: verifies field mapping changes take effect after reload
• reload_with_broken_pipeline_keeps_old_engine: verifies failed reload leaves old engine active
• Existing reload_rules_preserves_engine still passes
• Full workspace test suite passes (cargo test --workspace, zero failures)
• cargo clippy --workspace --all-features -- -D warnings clean