feat(ocr): add Kraken model download and evaluation script

Runbook script to download both HTR-United Kurrent model candidates
(german_kurrent_manu_9, kurrent-de) into the ocr_models Docker volume,
test them against sample documents, and activate the winner.

Usage:
  ./scripts/download-kraken-models.sh              # download both
  ./scripts/download-kraken-models.sh --activate 1  # pick model 1

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

scripts/download-kraken-models.sh

@@ -0,0 +1,89 @@
+#!/bin/bash
+set -euo pipefail
+
+# Downloads Kraken HTR models for German Kurrent/Suetterlin into the ocr_models volume.
+# Run this once after first deployment, or whenever you want to switch models.
+#
+# Usage:
+#   ./scripts/download-kraken-models.sh              # download both candidates
+#   ./scripts/download-kraken-models.sh --activate 1  # activate model 1 (german_kurrent_manu_9)
+#   ./scripts/download-kraken-models.sh --activate 2  # activate model 2 (kurrent-de)
+
+COMPOSE_SERVICE="ocr-service"
+MODEL_DIR="/app/models"
+ACTIVE_MODEL="$MODEL_DIR/german_kurrent.mlmodel"
+
+MODEL_1_NAME="german_kurrent_manu_9"
+MODEL_1_DESC="19th-century German administrative Kurrent (HTR-United)"
+MODEL_1_PATH="$MODEL_DIR/$MODEL_1_NAME.mlmodel"
+
+MODEL_2_NAME="kurrent-de"
+MODEL_2_DESC="Broad German Kurrent coverage (HTR-United)"
+MODEL_2_PATH="$MODEL_DIR/$MODEL_2_NAME.mlmodel"
+
+# ─── Functions ────────────────────────────────────────────────────────────────
+
+download_models() {
+    echo "Downloading Kraken HTR models into the ocr_models volume..."
+    echo ""
+
+    echo "Model 1: $MODEL_1_NAME"
+    echo "  $MODEL_1_DESC"
+    docker compose run --rm "$COMPOSE_SERVICE" \
+        kraken get "$MODEL_1_NAME" -o "$MODEL_1_PATH"
+    echo ""
+
+    echo "Model 2: $MODEL_2_NAME"
+    echo "  $MODEL_2_DESC"
+    docker compose run --rm "$COMPOSE_SERVICE" \
+        kraken get "$MODEL_2_NAME" -o "$MODEL_2_PATH"
+    echo ""
+
+    echo "Both models downloaded. To test them against a sample document:"
+    echo ""
+    echo "  # Copy a sample Kurrent scan into the container:"
+    echo "  docker cp sample-kurrent.png archive-ocr:/tmp/sample.png"
+    echo ""
+    echo "  # Test model 1:"
+    echo "  docker compose exec ocr-service kraken -i /tmp/sample.png /tmp/out1.txt segment -bl ocr -m $MODEL_1_PATH"
+    echo "  docker compose exec ocr-service cat /tmp/out1.txt"
+    echo ""
+    echo "  # Test model 2:"
+    echo "  docker compose exec ocr-service kraken -i /tmp/sample.png /tmp/out2.txt segment -bl ocr -m $MODEL_2_PATH"
+    echo "  docker compose exec ocr-service cat /tmp/out2.txt"
+    echo ""
+    echo "Then activate the better model:"
+    echo "  ./scripts/download-kraken-models.sh --activate 1   # or 2"
+}
+
+activate_model() {
+    local choice="$1"
+    case "$choice" in
+        1)
+            echo "Activating model 1: $MODEL_1_NAME"
+            docker compose run --rm "$COMPOSE_SERVICE" \
+                cp "$MODEL_1_PATH" "$ACTIVE_MODEL"
+            ;;
+        2)
+            echo "Activating model 2: $MODEL_2_NAME"
+            docker compose run --rm "$COMPOSE_SERVICE" \
+                cp "$MODEL_2_PATH" "$ACTIVE_MODEL"
+            ;;
+        *)
+            echo "Error: --activate expects 1 or 2"
+            exit 1
+            ;;
+    esac
+
+    echo "Active model is now: $ACTIVE_MODEL"
+    echo "Restart the OCR service to load the new model:"
+    echo "  docker compose restart ocr-service"
+}
+
+# ─── Main ─────────────────────────────────────────────────────────────────────
+
+if [[ "${1:-}" == "--activate" ]]; then
+    activate_model "${2:-}"
+else
+    download_models
+fi