[AZ-697] [AZ-702] tlog GPS truth + KHP20S30 factory calibration

Batch 98 (cycle 2) — first two PBIs of epic AZ-696 (real-flight
validation harness):

AZ-697: direct binary-tlog GPS-truth extractor

- New src/gps_denied_onboard/replay_input/tlog_ground_truth.py reads
  GLOBAL_POSITION_INT (with GPS_RAW_INT fallback) from a binary
  ArduPilot tlog via pymavlink.mavutil and returns a frozen+slotted
  TlogGroundTruth DTO with per-record ts_ns / lat_deg / lon_deg / alt_m
  / hdg_deg / vx_m_s / vy_m_s / vz_m_s.
- Promoted l2_horizontal_m + match_percentage + GroundTruthRow from
  tests/e2e/replay/_helpers.py into the new production module
  src/gps_denied_onboard/helpers/gps_compare.py. The e2e helper now
  re-exports the same objects (identity, not copies) so existing test
  imports continue working untouched.
- tests/e2e/replay/conftest.py prefers the real derkachi.tlog when
  present, falls back to the CSV synth path otherwise.
- 22 new unit tests cover AC-1..AC-5 (mypy --strict subprocess test
  included). All passing.

AZ-702: Topotek KHP20S30 factory-sheet camera calibration

- New _docs/00_problem/input_data/flight_derkachi/khp20s30_factory.json:
  fx = fy = 4644.444, cx = 960, cy = 540, HFOV ~ 23.3 deg, VFOV ~ 13.2
  deg, computed from the published 8.5 mm focal length + 1/2.8" sensor
  + 1920x1080 capture at lowest zoom step. Distortion zeroed,
  body_to_camera_se3 = identity with nadir convention. Acquisition
  method explicitly recorded as factory_sheet so downstream code can
  expect higher residual error than a lab calibration.
- _docs/00_problem/input_data/flight_derkachi/camera_info.md updated
  to document the assumptions, expected residual error window, and
  conftest pick-up rule.
- tests/e2e/replay/conftest.py::_calibration_path() prefers
  khp20s30_factory.json when present, falls back to adti26.json.
- 9 new unit tests cover AC-1..AC-4 (schema, intrinsics traceback,
  doc reference, conftest pick-up). All passing.

Test run: 45 new tests, all passing. Full-suite gate deferred to
Step 16 (after the last batch in cycle 2 per the implement skill).

Adjacent note (not fixed in this batch, recorded in the batch report):
auto_sync.py has the same redundant pymavlink type:ignore + a few
numpy/cv2 mypy --strict issues. None on this batch's path.

Refs: _docs/03_implementation/batch_98_cycle2_report.md
Refs: _docs/02_tasks/done/AZ-697_tlog_ground_truth_extractor.md
Refs: _docs/02_tasks/done/AZ-702_khp20s30_calibration.md

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

_docs/02_tasks/done/AZ-702_khp20s30_calibration.md

@@ -0,0 +1,106 @@
+# Topotek KHP20S30 camera calibration (factory-sheet approximation)
+
+**Task**: AZ-702_khp20s30_calibration
+**Name**: Provide a calibration JSON for the Topotek KHP20S30 nadir camera (factory-sheet approximation)
+**Description**: Compute and commit a `CameraCalibrationArtifact` JSON for the Derkachi camera (Topotek KHP20S30) from manufacturer factory data. Replaces the `adti26.json` placeholder that AC-3 currently uses. Documents the residual error vs a per-unit checkerboard refinement.
+**Complexity**: 1 point
+**Dependencies**: None
+**Component**: input_data / shared_helpers
+**Tracker**: AZ-702
+**Epic**: AZ-696
+
+## Problem
+
+`_docs/00_problem/input_data/flight_derkachi/camera_info.md` states the
+Topotek KHP20S30 intrinsics are unknown. `tests/e2e/replay/conftest.py`
+(line 50–56) substitutes `tests/fixtures/calibration/adti26.json` as a
+placeholder. AC-3 (≤ 100 m horizontal error for 80 % of ticks) is
+`@xfail` until a real calibration ships.
+
+The cheapest reasonable starting point is a factory-sheet approximation
+— compute `K` from the manufacturer's published focal length + sensor
+geometry, accept the 1–3 % focal-length residual as a documented
+budget, and let AC-3 either PASS or honestly FAIL with the residual
+attributed.
+
+## Outcome
+
+- A calibration JSON `khp20s30_factory.json` exists in the Derkachi
+  input directory, parses against the project's
+  `CameraCalibrationArtifact` schema, and documents the acquisition
+  method as `factory_sheet`.
+- `camera_info.md` is updated to reference the new calibration + the
+  residual budget + the deferral handle (`AZ-XXX_checkerboard_refinement`).
+- AZ-699 (T3) uses this calibration as its `--camera-calibration` input.
+
+## Scope
+
+### Included
+- Source manufacturer factory data for the Topotek KHP20S30 (sensor: 1/2.8" CMOS, 2.13 MP, 1920×1080; lens focal length, FOV, pixel pitch).
+- Compute `K = [[fx, 0, cx], [0, fy, cy], [0, 0, 1]]` from `fx = fy = focal_length_mm × (image_width_px / sensor_width_mm)`.
+- Set distortion to `[0, 0, 0, 0, 0]` (factory-sheet approximation).
+- Set `body_to_camera_se3` to identity-down (nadir; camera-z = aircraft-down).
+- Set `acquisition_method = "factory_sheet"`.
+- Write `_docs/00_problem/input_data/flight_derkachi/khp20s30_factory.json`.
+- Update `_docs/00_problem/input_data/flight_derkachi/camera_info.md`.
+- New unit test under `tests/unit/calibration/` asserting the JSON parses and matches the documented inputs.
+
+### Excluded
+- Physical checkerboard calibration (needs hardware).
+- PnP-from-tlog back-computation (deferred follow-up).
+- Updating `adti26.json` or other test fixtures.
+
+## Acceptance Criteria
+
+**AC-1: Calibration JSON parses**
+Given the new `khp20s30_factory.json`
+When loaded by the project's calibration parser (same schema as `adti26.json`)
+Then it parses without error and all fields are populated
+
+**AC-2: Doc updated**
+Given `camera_info.md` before
+When the calibration is committed
+Then `camera_info.md` says "factory-sheet approximation; per-unit checkerboard refinement deferred — see <future-task>" and lists the residual budget
+
+**AC-3: Unit test snapshot**
+Given the new JSON
+When the unit test runs
+Then it asserts `fx == fy` (square pixels), `cx ≈ width/2`, `cy ≈ height/2`, distortion all zero
+
+**AC-4: T3 consumes this calibration**
+Given AZ-699's `test_derkachi_real_tlog.py`
+When it runs
+Then it loads `khp20s30_factory.json` as `--camera-calibration` (no longer the `adti26.json` placeholder)
+
+## Non-Functional Requirements
+
+**Compatibility**
+- JSON schema MUST be identical to existing calibration fixtures (`adti26.json`) — no schema changes in this task.
+
+## Unit Tests
+
+| AC Ref | What to Test | Required Outcome |
+|--------|-------------|-----------------|
+| AC-1 | JSON loads via existing parser | Object populated |
+| AC-3 | Field values match factory inputs | fx == fy, cx/cy at centre, zero distortion |
+
+## Blackbox Tests
+
+| AC Ref | Initial Data/Conditions | What to Test | Expected Behavior | NFR References |
+|--------|------------------------|-------------|-------------------|----------------|
+| AC-4 | T3 test pointed at new JSON | T3 launches without calibration parse error | Test starts cleanly | Compat |
+
+## Constraints
+
+- MUST follow the calibration contract in `_docs/02_document/contracts/shared_helpers/descriptor_normaliser.md` (or wherever the camera-calibration schema lives).
+- MUST be a single committed JSON — no generator script with side effects.
+
+## Risks & Mitigation
+
+**Risk 1: Factory data unavailable at required precision**
+- *Risk*: Topotek does not publish the exact focal length / sensor width to the precision needed.
+- *Mitigation*: Document the gap; ship with the best-available estimate; flag in `camera_info.md` so T3 surfaces the uncertainty in its failure message.
+
+**Risk 2: Residual error exceeds AC-3 budget**
+- *Risk*: 1–3 % focal-length error may push horizontal error past 100 m at 1 km AGL.
+- *Mitigation*: That's the honest finding. T3 reports it. A follow-up task can pursue checkerboard refinement if needed.