feat: add Timestamp PDF tool with RFC 3161 support

Add document timestamping to the Secure PDF section using RFC 3161
protocol. Users can select from preset TSA servers (DigiCert, Sectigo,
SSL.com, Entrust, FreeTSA) or enter a custom TSA URL. No personal
certificate is required — only a cryptographic hash is sent to the server.

Key changes:
- Timestamp PDF page with TSA server selector, FAQ and SEO structured data
- timestampPdf() function with CORS proxy URL resolution
- TimestampNode for the workflow engine
- Tool entry in Secure PDF category + homepage i18n
- Built-in CORS proxy middleware for dev/preview
- Translations for all 16 languages

Tested with DigiCert, Sectigo and Entrust TSA servers. Timestamps are
verifiable in Adobe Acrobat (ETSI.RFC3161 SubFilter).

public/locales/sv/tools.json

@@ -593,6 +593,15 @@
     "pageTitle": "Validera PDF-signatur - Verifiera digitala signaturer | BentoPDF",
     "subtitle": "Verifiera digitala signaturer i dina PDF-filer. Kontrollera certifikatgiltighet, visa signerardetaljer och bekräfta dokumentintegritet. All bearbetning sker i din webbläsare."
   },
+  "timestampPdf": {
+    "name": "Tidsstämpla PDF",
+    "pageTitle": "Tidsstämpla PDF gratis online - RFC 3161 dokumenttidsstämpel | BentoPDF",
+    "subtitle": "Lägg till en RFC 3161 tidsstämpel till din PDF via en betrodd TSA-server. Bevisar att ditt dokument existerade vid en specifik tidpunkt. Inget certifikat krävs.",
+    "tsaSectionTitle": "Tidsstämpelserver (TSA)",
+    "selectTsa": "Välj en TSA-server",
+    "applyTimestamp": "Tillämpa tidsstämpel",
+    "successMessage": "PDF tidsstämplad! Tidsstämpeln kan verifieras i Adobe Acrobat och andra PDF-läsare."
+  },
   "emailToPdf": {
     "name": "E-post till PDF",
     "subtitle": "Konvertera e-postfiler (EML, MSG) till PDF-format. Stöder Outlook-exporter och standard e-postformat.",