feat: FASE 6.5 - Report PDF (WeasyPrint + Kaleido)

Add PDF report generation for Metrologist dashboard with SPC and
measurement reports including SVG charts, capability indices, and
company logo embedding.

New files:
- server/services/report_service.py (Jinja2 + Plotly/Kaleido + WeasyPrint)
- server/routers/reports.py (2 GET endpoints with auth)
- server/templates/reports/ (base, spc, measurement HTML templates)

Modified:
- server/main.py (register reports router)
- client dashboard (download buttons + proxy routes)
- i18n strings IT/EN

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

client/blueprints/statistics.py

@@ -1,8 +1,11 @@
 """Metrologist blueprint - SPC statistics dashboard and API proxies."""
-from flask import Blueprint, jsonify, render_template, request
+import requests as http_requests
+
+from flask import Blueprint, jsonify, render_template, request, session
 from flask_babel import gettext as _
 
 from blueprints.auth import login_required, role_required
+from config import Config
 from services.api_client import api_client
 
 statistics_bp = Blueprint("statistics", __name__)
@@ -105,3 +108,71 @@ def api_subtasks():
         return jsonify(resp)
 
     return jsonify(resp)
+
+
+# ============================================================================
+# PROXY REPORT PDF → FastAPI
+# ============================================================================
+
+def _proxy_report(endpoint: str):
+    """Forward query params to a FastAPI reports endpoint and return PDF."""
+    params = {}
+    for key in [
+        "recipe_id", "version_id", "subtask_id",
+        "date_from", "date_to", "operator_id",
+        "lot_number", "serial_number",
+    ]:
+        val = request.args.get(key)
+        if val is not None and val != "":
+            params[key] = val
+
+    base_url = Config.API_SERVER_URL.rstrip("/")
+    headers = {}
+    api_key = session.get("api_key")
+    if api_key:
+        headers["X-API-Key"] = api_key
+
+    try:
+        resp = http_requests.get(
+            f"{base_url}/api/reports/{endpoint}",
+            headers=headers,
+            params=params,
+            timeout=120,
+        )
+    except (http_requests.ConnectionError, http_requests.Timeout) as e:
+        return jsonify({"error": True, "detail": str(e)}), 502
+
+    if not resp.ok:
+        try:
+            err = resp.json()
+            detail = err.get("detail", f"HTTP {resp.status_code}")
+        except Exception:
+            detail = f"HTTP {resp.status_code}"
+        return jsonify({"error": True, "detail": detail}), resp.status_code
+
+    from flask import Response as FlaskResponse
+    return FlaskResponse(
+        resp.content,
+        mimetype="application/pdf",
+        headers={
+            "Content-Disposition": resp.headers.get(
+                "Content-Disposition", f'attachment; filename="report.pdf"'
+            )
+        },
+    )
+
+
+@statistics_bp.route("/api/report-spc")
+@login_required
+@role_required("Metrologist")
+def api_report_spc():
+    """Proxy: download SPC PDF report."""
+    return _proxy_report("spc")
+
+
+@statistics_bp.route("/api/report-measurements")
+@login_required
+@role_required("Metrologist")
+def api_report_measurements():
+    """Proxy: download measurements PDF report."""
+    return _proxy_report("measurements")