chore: run go fix for Go 1.26 modernization

106 files: interface{}→any, strings.Split→SplitSeq, CutPrefix/Cut, strings.Builder, slices.Contains, remove redundant // +build directives, gofmt import ordering and indentation.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

backend/internal/dav/service_dev.go

@@ -1,5 +1,4 @@
 //go:build dev
-// +build dev
 
 package dav
 

backend/internal/dav/service_prod.go

@@ -1,5 +1,4 @@
 //go:build !dev
-// +build !dev
 
 package dav
 

backend/internal/dav/shared.go

@@ -1,8 +1,8 @@
 package dav
 
 import (
-	"crussell/clock"
 	"context"
+	"crussell/clock"
 	"fmt"
 	"strings"
 	"time"
@@ -131,7 +131,7 @@ func (s *BaseService) ListRecentContacts(days int) ([]Contact, error) {
 // Helper Methods
 // ============================================================================
 
-func (s *BaseService) queryEventsWithContacts(query string, args ...interface{}) ([]CalendarEvent, error) {
+func (s *BaseService) queryEventsWithContacts(query string, args ...any) ([]CalendarEvent, error) {
 	rows, err := s.db.Query(context.Background(), query, args...)
 	if err != nil {
 		return nil, err
@@ -155,7 +155,7 @@ func (s *BaseService) queryEventsWithContacts(query string, args ...interface{})
 
 func extractContactURIsFromICalendar(icalData string) []string {
 	var uris []string
-	for _, line := range strings.Split(icalData, "\n") {
+	for line := range strings.SplitSeq(icalData, "\n") {
 		line = strings.TrimSpace(line)
 		if strings.HasPrefix(line, "ATTENDEE") {
 			parts := strings.Split(line, ":")

backend/internal/dav/types.go

@@ -3,6 +3,7 @@ package dav
 import (
 	"crussell/clock"
 	"fmt"
+	"strings"
 	"time"
 )
 
@@ -102,9 +103,9 @@ func GenerateICalEvent(input EventInput) string {
 	}
 
 	// Build attendees section
-	attendees := ""
+	var attendees strings.Builder
 	for _, contactURI := range input.ContactURIs {
-		attendees += fmt.Sprintf("ATTENDEE;CN=%s:%s\n", contactURI, contactURI)
+		attendees.WriteString(fmt.Sprintf("ATTENDEE;CN=%s:%s\n", contactURI, contactURI))
 	}
 
 	ical := fmt.Sprintf(`BEGIN:VCALENDAR
@@ -127,7 +128,7 @@ END:VCALENDAR`, uid, dtstamp, dtstart, dtend,
 		escapeICalText(input.Summary),
 		escapeICalText(input.Description),
 		escapeICalText(input.Location),
-		attendees)
+		attendees.String())
 
 	return ical
 }
@@ -164,13 +165,13 @@ func escapeICalText(text string) string {
 }
 
 func replaceAll(s, old, new string) string {
-	result := ""
+	var result strings.Builder
 	for _, char := range s {
 		if string(char) == old {
-			result += new
+			result.WriteString(new)
 		} else {
-			result += string(char)
+			result.WriteString(string(char))
 		}
 	}
-	return result
+	return result.String()
 }

backend/internal/images/validate_test.go

@@ -1,5 +1,4 @@
 //go:build test
-// +build test
 
 package images
 

backend/internal/s3/s3.go

@@ -1,5 +1,4 @@
 //go:build !dev
-// +build !dev
 
 package s3
 

backend/internal/s3/s3_dev.go

@@ -1,5 +1,4 @@
 //go:build dev
-// +build dev
 
 package s3
 

backend/internal/square/square.go

@@ -1,5 +1,4 @@
 //go:build !dev
-// +build !dev
 
 package square
 

backend/internal/square/square_dev.go

@@ -1,11 +1,10 @@
 //go:build dev
-// +build dev
 
 package square
 
 import (
-	"crussell/clock"
 	"context"
+	"crussell/clock"
 	"fmt"
 	"log"
 	"os"

backend/internal/square/square_dev_test.go

@@ -1,5 +1,4 @@
 //go:build test && dev
-// +build test,dev
 
 package square
 

backend/internal/validators/email.go

@@ -30,11 +30,11 @@ func ValidateEmail(email string) error {
 
 // NormalizeGiftCardCode strips non-alphanumeric characters and upper-cases the code.
 func NormalizeGiftCardCode(code string) string {
-	clean := ""
+	var clean strings.Builder
 	for _, char := range code {
 		if (char >= 'a' && char <= 'z') || (char >= 'A' && char <= 'Z') || (char >= '0' && char <= '9') {
-			clean += string(char)
+			clean.WriteString(string(char))
 		}
 	}
-	return clean
+	return clean.String()
 }

backend/internal/validators/email_test.go

@@ -1,5 +1,4 @@
 //go:build test
-// +build test
 
 package validators