update docs

docs/architecture/03-detection-pipeline.dot

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+digraph detection_pipeline {
+    rankdir=TB
+    bgcolor="#0a0e17"
+    fontname="Helvetica"
+    node [fontname="Helvetica" fontsize=11 style=filled color="#1e2a4a" fontcolor="#e8eaf0" shape=box]
+    edge [fontname="Helvetica" fontsize=9 fontcolor="#8892a8" color="#4a5568"]
+
+    label="Detection Pipeline (core/detect/graph/nodes.py)"
+    labelloc=t
+    fontsize=16
+    fontcolor="#0066ff"
+
+    extract_frames    [label="extract_frames\n(ffmpeg, fps from profile)" fillcolor="#121829"]
+    filter_scenes     [label="filter_scenes\n(scene-change filter)" fillcolor="#121829"]
+
+    field_seg         [label="field_segmentation\n(HSV mask · GPU/WASM)" fillcolor="#0d1a33" fontcolor="#0066ff"]
+    detect_edges      [label="detect_edges\n(Canny + Hough · GPU/WASM)" fillcolor="#0d1a33" fontcolor="#0066ff"]
+
+    detect_objects    [label="detect_objects\n(YOLO · GPU)" fillcolor="#1a3a1a" fontcolor="#00c853"]
+    preprocess        [label="preprocess\n(crop · contrast · deskew)" fillcolor="#121829"]
+    run_ocr           [label="run_ocr\n(OCR · GPU)" fillcolor="#1a3a1a" fontcolor="#00c853"]
+
+    match_brands      [label="match_brands\n(rapidfuzz vs session)" fillcolor="#121829"]
+    escalate_vlm      [label="escalate_vlm\n(local VLM · GPU)" fillcolor="#1a3a1a" fontcolor="#00c853"]
+    escalate_cloud    [label="escalate_cloud\n(Anthropic · Gemini\nOpenAI · Groq)" fillcolor="#243056" shape=octagon]
+
+    compile_report    [label="compile_report\n(timeline + brand stats)" fillcolor="#0d1a33" fontcolor="#0066ff"]
+
+    extract_frames -> filter_scenes
+    filter_scenes  -> field_seg
+    filter_scenes  -> detect_objects
+    field_seg      -> detect_edges       [label="masks"]
+    detect_edges   -> detect_objects     [style=dashed label="region hints"]
+    detect_objects -> preprocess         [label="boxes"]
+    preprocess     -> run_ocr
+    run_ocr        -> match_brands       [label="text candidates"]
+    match_brands   -> escalate_vlm       [label="unresolved"]
+    escalate_vlm   -> escalate_cloud     [label="still unresolved"]
+    match_brands   -> compile_report
+    escalate_vlm   -> compile_report
+    escalate_cloud -> compile_report
+}