[AZ-219] Scaffold onboard runtime project

Add the initial source, test, infrastructure, CI, configuration, and evidence-path scaffold so dependent implementation tasks have stable package and runtime boundaries.

Co-authored-by: Cursor <cursoragent@cursor.com>

src/fdr_observability/interfaces.py

@@ -0,0 +1,13 @@
+"""Public flight recorder interfaces."""
+
+from typing import Any, Protocol
+
+
+class FlightRecorder(Protocol):
+    """Append-only event recorder for runtime evidence."""
+
+    def append_event(self, event: Any) -> None:
+        """Persist one FDR event."""
+
+    def export(self) -> Any:
+        """Export recorded evidence for post-flight analysis."""