[AZ-698] Multi-flight tlog handling: segment first, pick last flight

Real derkachi.tlog covers 3 takeoffs at the same field but the
uploaded video covers only the last. Original NCC argmax + AZ-405
head-takeoff fallback both biased toward flight 1, violating the
spec's "the last chunk in tlog is relevant" framing.

Patch: pre-NCC flight segmenter partitions the IMU energy stream
into distinct flights (threshold + gap walk); find_aligned_window
restricts NCC search to the last segment; low-confidence fallback
uses that segment's start instead of head-takeoff detection.
AlignedWindow gains flight_count_detected + selected_flight_index
for FDR-visible audit.

7 new unit tests (segmenter shapes + end-to-end multi-flight
pipeline + segmented fallback path). 19 AZ-698 tests pass, 113
in the regression slice. Zero new mypy --strict errors.

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

src/gps_denied_onboard/replay_input/tlog_video_adapter.py

@@ -476,10 +476,14 @@ class ReplayInputAdapter:
             "offset_ms": window.offset_ms,
             "confidence": window.confidence,
             "fallback_used": window.fallback_used,
+            "flight_count_detected": window.flight_count_detected,
+            "selected_flight_index": window.selected_flight_index,
         }
         msg = (
             f"{kind}: tlog_start_ns={window.tlog_start_ns} "
-            f"offset_ms={window.offset_ms} confidence={window.confidence:.3f}"
+            f"offset_ms={window.offset_ms} confidence={window.confidence:.3f} "
+            f"flights_detected={window.flight_count_detected} "
+            f"selected_flight={window.selected_flight_index}"
         )
         if window.fallback_used:
             self._log.warning(msg, extra={"kind": kind, "kv": kv})