feat: Umstellung auf Anthropic Claude SDK, Rechnungsgenerator-Systemtemplate und Task-Status-Sync

- LLM-Integration von LM Studio (Spring AI OpenAI) auf Anthropic Java SDK umgestellt
- Rechnungsgenerator: System-Template für Rechnungen an Nutzer, Canvas leeren, PDF-Vorschau
- Job manuell beenden sendet job_deleted an verbundene App-Clients
- MessageController: nur offene Jobs ausliefern, station_completed per jobId auflösen
- App: Task-Erledigungsstatus aus Server-Tasks auf Stations-Snapshots übernehmen, lokale Task-Status bei Offline-Pufferung erhalten
- Adressbuch-Wording in allen Sprachdateien, Version 0.9.18

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

backend/src/main/resources/messages_en.properties

@@ -241,7 +241,7 @@ page.title.dashboard=VotianLT - Dashboard
 page.title.appuser.create=Create New App User
 page.title.messages=Messages
 page.title.register=Register at VotianLT
-page.title.customers=Customers
+page.title.customers=Address Book
 page.title.customer.edit=Edit Customer
 page.title.verwaltung=Management
 page.title.company.create=Create New Company
@@ -249,7 +249,7 @@ page.title.imprint=Imprint
 page.title.profile.edit=Edit Profile
 page.title.admin.dashboard=Admin Dashboard
 page.title.invoice.create=Create Invoice
-page.title.customer.create=Create New Customer
+page.title.customer.create=Create New Address
 page.title.login=Log In to VotianLT
 page.title.jobs=Jobs
 page.title.appuser.edit=Edit App User
@@ -328,9 +328,9 @@ editappuser.dialog.delete.text=Are you sure you want to delete this app user?
 editappuser.dialog.delete.confirm=Delete
 
 # Customers
-customers.title=Customers
-customers.button.add=Add New Customer
-customers.hint.click=Click on a customer to see details
+customers.title=Address Book
+customers.button.add=Add New Address
+customers.hint.click=Click on an address entry to see details
 customers.column.company=Company
 customers.column.name=Name
 customers.column.email=Email
@@ -349,8 +349,8 @@ editcustomer.dialog.delete.text=Are you sure you want to delete this customer?
 editcustomer.dialog.delete.confirm=Delete
 
 # Add Customer
-addcustomer.title=Create New Customer
-addcustomer.button.submit=Create Customer
+addcustomer.title=Create New Address
+addcustomer.button.submit=Create Address
 addcustomer.notification.validation=Please fill in all required fields
 addcustomer.notification.success=Customer created successfully
 addcustomer.notification.check=Please check your input
@@ -1056,3 +1056,24 @@ adminpricetable.field.revenue=Revenue Share
 adminpricetable.notification.saved=Price table has been saved
 adminpricetable.notification.save.error=Error saving: {0}
 adminpricetable.notification.load.error=Error loading: {0}
+
+# Invoice generator - system template (invoices to users)
+invoicegenerator.issuer.header=Invoice issuer
+invoicegenerator.issuer.website=Website
+invoicegenerator.issuer.senderline=Sender line
+invoicegenerator.issuer.paymentterms=Payment terms
+invoicegenerator.issuer.footer=Footer
+invoicegenerator.issuer.invoicedate=Invoice date
+invoicegenerator.recipient.header=Recipient (user)
+invoicegenerator.recipient.company=User company
+invoicegenerator.recipient.name=User name
+invoicegenerator.recipient.street=User street
+invoicegenerator.recipient.city=User city
+invoicegenerator.recipient.email=User email
+invoicegenerator.template.saved=Template saved
+invoicegenerator.template.save.error=Error saving template: {0}
+invoicegenerator.button.clear=Clear
+invoicegenerator.notification.cleared=Canvas cleared
+invoicegenerator.notification.canvas.error=Could not read canvas data
+invoicegenerator.notification.preview.error=Preview error: {0}
+invoicegenerator.pdf.preview.title=PDF preview