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/translations/en/LC_MESSAGES/messages.po

@@ -1038,3 +1038,13 @@ msgstr "Normal curve"
 
 msgid "Indici non disponibili"
 msgstr "Indices not available"
+
+# Report PDF
+msgid "Report SPC"
+msgstr "SPC Report"
+
+msgid "Report Misurazioni"
+msgstr "Measurements Report"
+
+msgid "Errore nella generazione del report"
+msgstr "Error generating report"

client/translations/it/LC_MESSAGES/messages.po

@@ -1038,3 +1038,13 @@ msgstr "Curva normale"
 
 msgid "Indici non disponibili"
 msgstr "Indici non disponibili"
+
+# Report PDF
+msgid "Report SPC"
+msgstr "Report SPC"
+
+msgid "Report Misurazioni"
+msgstr "Report Misurazioni"
+
+msgid "Errore nella generazione del report"
+msgstr "Errore nella generazione del report"