Use stable files API URLs for vendor logo fields

CommonThirdParty.logoUrl and TrustCenterReference.logoUrl were
returning expiring S3 presigned URLs, which break if cached or
shared past their TTL.

Replace with stable /api/files/v1/{id} application URLs.
file.Service now generates these via baseurl; a new filesign
package owns presigning for the files/v1 HTTP handler that
does the internal redirect.

Signed-off-by: Ludovic Vielle <ludovic@probo.com>

pkg/filesign/service.go

@@ -0,0 +1,62 @@
+// Copyright (c) 2026 Probo Inc <hello@getprobo.com>.
+//
+// Permission to use, copy, modify, and/or distribute this software for any
+// purpose with or without fee is hereby granted, provided that the above
+// copyright notice and this permission notice appear in all copies.
+//
+// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+// REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+// AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+// INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+// LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+// OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+// PERFORMANCE OF THIS SOFTWARE.
+
+package filesign
+
+import (
+	"context"
+	"fmt"
+	"time"
+
+	"go.gearno.de/kit/pg"
+	"go.probo.inc/probo/pkg/coredata"
+	"go.probo.inc/probo/pkg/filemanager"
+	"go.probo.inc/probo/pkg/gid"
+)
+
+type Service struct {
+	pg          *pg.Client
+	fileManager *filemanager.Service
+}
+
+func NewService(pgClient *pg.Client, fileManager *filemanager.Service) *Service {
+	return &Service{
+		pg:          pgClient,
+		fileManager: fileManager,
+	}
+}
+
+// GeneratePresignedFileURL returns a short-lived S3 presigned URL for a PUBLIC file.
+// Prefer file.Service.GenerateFileURL in most cases — it returns a stable, cacheable
+// application URL. Only use this when a direct S3 URL with a controlled TTL is required
+// (e.g. the /api/files/v1 HTTP handler that issues the presign-on-redirect).
+func (s *Service) GeneratePresignedFileURL(
+	ctx context.Context,
+	fileID gid.GID,
+	expiresIn time.Duration,
+) (string, error) {
+	file := &coredata.File{}
+
+	err := s.pg.WithConn(ctx, func(ctx context.Context, conn pg.Querier) error {
+		if err := file.LoadPublicByID(ctx, conn, fileID); err != nil {
+			return fmt.Errorf("cannot load public file: %w", err)
+		}
+		return nil
+	})
+	if err != nil {
+		return "", err
+	}
+
+	return s.fileManager.GenerateFileUrl(ctx, file, expiresIn)
+}