Add printer lifecycle fields and printer log

- Printer: bought_at, last_maintenance_at, decommissioned_at (all Date, nullable)
- PrinterLog: per-printer timestamped text entries (CASCADE delete)
- Migration 0003: adds columns + printer_logs table
- /printers/{id}: detail page showing lifecycle info + scrollable log
- POST /printers/{id}/log: add a log entry via modal form
- Printer names in list are now links to the detail page
- Add Printer modal includes optional purchase date

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

app/models/__init__.py

@@ -3,7 +3,8 @@ from app.models.filament import Filament
 from app.models.pricing import PricingConfig
 from app.models.print_job import PrintJob
 from app.models.printer import Printer
+from app.models.printer_log import PrinterLog
 from app.models.printer_type import PrinterType
 from app.models.todo import Todo
 
-__all__ = ["Base", "Printer", "PrinterType", "Filament", "PrintJob", "Todo", "PricingConfig"]
+__all__ = ["Base", "Printer", "PrinterLog", "PrinterType", "Filament", "PrintJob", "Todo", "PricingConfig"]