feat(02-07): add Pydantic v2 boundary-log schemas (OBS-01)

- Create src/gps_denied/obs/log_schemas.py with 3 models:
  MavlinkGpsInputEmitted (AC-4.3 + AC-1.4), ApiRequestCompleted,
  AnchorDecision (VERIFY-02)
- All models use ConfigDict(extra='forbid', frozen=True)
- SourceLabel Literal encodes AC-1.4 vocab; AnchorRejectReason encodes VERIFY-02
- Update gps_denied.obs barrel __init__.py to re-export all schemas + type aliases

src/gps_denied/obs/__init__.py

@@ -0,0 +1,30 @@
+"""Observability package — structlog spine + boundary log schemas.
+
+Hot-path logging spine wired by ``configure_logging``; per-frame ``correlation_id``
+(= frame_id) bound at ``pipeline/orchestrator.py:process_frame``.
+
+Boundary log schemas (REST, FDR, anchor decisions) defined in ``log_schemas``.
+"""
+import structlog
+
+from gps_denied.obs.log_schemas import (
+    AnchorDecision,
+    AnchorRejectReason,
+    ApiRequestCompleted,
+    MavlinkGpsInputEmitted,
+    SourceLabel,
+)
+from gps_denied.obs.logging_config import configure_logging
+
+get_logger = structlog.get_logger  # convenience re-export
+
+__all__ = [
+    "configure_logging",
+    "get_logger",
+    # Boundary schemas
+    "MavlinkGpsInputEmitted",
+    "ApiRequestCompleted",
+    "AnchorDecision",
+    "SourceLabel",
+    "AnchorRejectReason",
+]