Rebrand from MyCrib to Casera

- Update Go module from mycrib-api to casera-api
- Update all import statements across 69 Go files
- Update admin panel branding (title, sidebar, login form)
- Update email templates (subjects, bodies, signatures)
- Update PDF report generation branding
- Update Docker container names and network
- Update config defaults (database name, email sender, APNS topic)
- Update README and documentation

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

internal/services/pdf_service.go

@@ -164,7 +164,7 @@ func (s *PDFService) GenerateTasksReportPDF(report *TasksReportResponse) ([]byte
 	pdf.SetY(-25)
 	pdf.SetFont("Arial", "I", 9)
 	pdf.SetTextColor(128, 128, 128)
-	pdf.Cell(0, 10, fmt.Sprintf("MyCrib - Tasks Report for %s", report.ResidenceName))
+	pdf.Cell(0, 10, fmt.Sprintf("Casera - Tasks Report for %s", report.ResidenceName))
 	pdf.Ln(5)
 	pdf.Cell(0, 10, fmt.Sprintf("Generated on %s", time.Now().UTC().Format("2006-01-02 15:04:05 UTC")))