feat(gpr): explicitly mark GlobalPlaceRecognition as AnyLoc-VLAD-DINOv2 baseline

GlobalPlaceRecognition already implements AnyLoc-VLAD-DINOv2 (existing code).
This change makes the sprint 1 GPR technology selection explicit:

- Expand class docstring with selection rationale vs NetVLAD / SP+LG
- Document INT8 quantization as known-broken for ViT on Jetson
- Reference design doc §2.3 and stage2 backlog
- Add two marker tests asserting 4096-d descriptor + DINOv2 engine name

No behavioral change — existing Mock/TRT path unchanged.
Ref: docs/superpowers/specs/2026-04-18-oss-stack-tech-audit-design.md §2.3

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/gps_denied/core/gpr.py

@@ -62,12 +62,21 @@ class IGlobalPlaceRecognition(ABC):
 
 
 class GlobalPlaceRecognition(IGlobalPlaceRecognition):
-    """AnyLoc (DINOv2) coarse localisation component.
+    """AnyLoc-VLAD-DINOv2 coarse localisation component — sprint 1 GPR baseline.
 
     GPR-01: load_index() tries to open a real Faiss .index file; falls back to
             a NumPy L2 mock when the file is missing or Faiss is not installed.
-    GPR-02: Descriptor computed via DINOv2 engine (TRT on Jetson, Mock on dev/CI).
+    GPR-02: Descriptor computed via DINOv2 engine (TRT FP16 on Jetson, Mock on
+            dev/CI). INT8 quantization is disabled — broken for ViT on Jetson
+            (NVIDIA/TRT#4348, facebookresearch/dinov2#489).
     GPR-03: Candidates ranked by descriptor similarity (L2 → converted to [0,1]).
+
+    Selected over NetVLAD (deprecated, −2.4% R@1 on MSLS 2024) and SuperPoint+
+    LightGlue (unvalidated for cross-view UAV↔satellite gap at sprint 1).
+    Stage 2 evaluation: SP+LG+FAISS per _docs/03_backlog/stage2_ideas/.
+    Long-term target: EigenPlaces (ICCV 2023) — cleaner ONNX export.
+
+    Ref: docs/superpowers/specs/2026-04-18-oss-stack-tech-audit-design.md §2.3
     """
 
     _DIM = 4096  # DINOv2 VLAD descriptor dimension