feat: add user centric features

internal/service/user_service.go

@@ -24,7 +24,7 @@ func NewUserService(users *repository.UserRepo, r2 *repository.R2) *UserService
 	return &UserService{users: users, r2: r2}
 }
 
-// UpdateProfile updates the user's name and/or avatar URL.
+// UpdateProfile updates the user's name, avatar URL, and/or handle.
 //
 // `avatarURL` semantics:
 //
@@ -32,10 +32,10 @@ func NewUserService(users *repository.UserRepo, r2 *repository.R2) *UserService
 //	""   → clear (remove avatar)
 //	"x"  → set to "x"
 //
-// The avatar URL is expected to point at our R2 bucket — we don't validate
-// the host because we don't want to break tests / local setups, but in
-// production you could add a check that it starts with R2_PUBLIC_URL.
-func (s *UserService) UpdateProfile(ctx context.Context, id string, name *string, avatarURL *string) (*model.User, error) {
+// `handle` is normalized to the project's slug format before being passed
+// to the DB so users can't sneak in spaces or punctuation. Empty after
+// normalization → 400.
+func (s *UserService) UpdateProfile(ctx context.Context, id string, name, avatarURL, handle *string) (*model.User, error) {
 	if name != nil {
 		trimmed := strings.TrimSpace(*name)
 		if trimmed == "" {
@@ -46,7 +46,38 @@ func (s *UserService) UpdateProfile(ctx context.Context, id string, name *string
 		}
 		name = &trimmed
 	}
-	return s.users.UpdateProfile(ctx, id, name, avatarURL)
+	if handle != nil {
+		clean := normalizeHandle(*handle)
+		if len(clean) < 3 {
+			return nil, errors.New("handle must be at least 3 characters (letters, digits, dashes)")
+		}
+		if len(clean) > 32 {
+			return nil, errors.New("handle too long (max 32)")
+		}
+		handle = &clean
+	}
+	return s.users.UpdateProfile(ctx, id, name, avatarURL, handle)
+}
+
+// normalizeHandle lowercases and strips anything that isn't [a-z0-9-]. Same
+// rules as slugForHandle in auth_service, but exposed here because the
+// profile-update path doesn't go through auth.
+func normalizeHandle(raw string) string {
+	var b strings.Builder
+	for _, r := range strings.ToLower(strings.TrimSpace(raw)) {
+		switch {
+		case r >= 'a' && r <= 'z', r >= '0' && r <= '9':
+			b.WriteRune(r)
+		case r == '-', r == '.', r == '_':
+			b.WriteByte('-')
+		}
+	}
+	out := strings.Trim(b.String(), "-")
+	// Collapse runs of dashes.
+	for strings.Contains(out, "--") {
+		out = strings.ReplaceAll(out, "--", "-")
+	}
+	return out
 }
 
 // AvatarPresign issues a one-shot presigned PUT URL the frontend uses to