[AZ-701] HTTP replay API service (FastAPI + magic-byte upload validation)

New replay_api component: FastAPI service wrapping the offline
gps-denied-replay pipeline. POST tlog+video (multipart) → either
sync 200 with result/map/report URLs, or async 202 + job id with
/jobs/{id} polling. Magic-byte validation, bearer auth, in-memory
JobRegistry with concurrency + queue caps (429 on overflow).

Helper accuracy_report.py promoted from tests/ to src/ because the
API needs the Markdown report writer at runtime; all AZ-699 imports
re-pointed. OpenAPI spec exported to docs.

18/18 unit tests pass (AC-1 sync, AC-2 async, AC-3 state machine,
AC-5 auth, AC-6 health, AC-8 concurrency, AC-9 magic-byte). Full
unit suite: 2251 pass, 86 skip, 1 pre-existing C12 cold-start flake
(unchanged). mypy --strict clean on the new surface.

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

src/gps_denied_onboard/helpers/__init__.py

@@ -16,6 +16,14 @@ from gps_denied_onboard.helpers.engine_filename_schema import (
     EngineFilenameSchema,
     EngineFilenameSchemaError,
 )
+from gps_denied_onboard.helpers.accuracy_report import (
+    AC3_GATE_PCT,
+    AC3_GATE_THRESHOLD_M,
+    ReportContext,
+    format_failure_message,
+    render_report,
+    verdict_passes_ac3,
+)
 from gps_denied_onboard.helpers.gps_compare import (
     GroundTruthRow,
     HorizontalErrorDistribution,
@@ -67,10 +75,13 @@ from gps_denied_onboard.helpers.wgs_converter import (
 )
 
 __all__ = [
+    "AC3_GATE_PCT",
+    "AC3_GATE_THRESHOLD_M",
     "ALLOWED_DTYPES",
     "ALLOWED_PRECISIONS",
     "ENGINE_SUFFIX",
     "MAX_ZOOM",
+    "ReportContext",
     "SE3",
     "SIDECAR_SUFFIX",
     "WEB_MERCATOR_MAX_LAT_DEG",
@@ -96,6 +107,7 @@ __all__ = [
     "WgsConverter",
     "adjoint",
     "exp_map",
+    "format_failure_message",
     "horizontal_error_distribution",
     "is_valid_rotation",
     "iso_ts_from_clock",
@@ -106,5 +118,7 @@ __all__ = [
     "make_imu_preintegrator",
     "matrix_to_se3",
     "percentile_sorted",
+    "render_report",
     "se3_to_matrix",
+    "verdict_passes_ac3",
 ]