feat(aether): initial commit – self-hosted Cloud, Phasen 1–7

Go-Backend (chi, pgx, golang-migrate) + React/TS-Frontend als PWA.
Enthalten: Auth inkl. OIDC, Dateien mit Versionen und Papierkorb,
Freigaben (Links + intern), WebDAV, Gruppenordner, Admin/Theming,
Volltextsuche mit OCR, eigener PDF-Betrachter und WOPI-Office
(Collabora/OnlyOffice).

Nicht im Repo: deploy/.env (Sitzungsschlüssel, DB- und Admin-Passwort)
sowie alle Daten- und Build-Verzeichnisse – siehe .gitignore.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

backend/internal/thumbnails/thumbnails.go

@@ -0,0 +1,95 @@
+package thumbnails
+
+import (
+	"bytes"
+	"context"
+	"fmt"
+	"image"
+	_ "image/gif"
+	"image/jpeg"
+	_ "image/png"
+
+	_ "golang.org/x/image/webp" // SupportedMIME nennt WebP – ohne den Dekodierer entstand dafür nie ein Vorschaubild
+	"io"
+	"strings"
+
+	"golang.org/x/image/draw"
+
+	"aether/internal/storage"
+)
+
+const (
+	maxWidth  = 256
+	maxHeight = 256
+)
+
+// SupportedMIME returns true if we can generate a thumbnail for this MIME type.
+func SupportedMIME(mime string) bool {
+	m := strings.ToLower(mime)
+	return strings.HasPrefix(m, "image/jpeg") ||
+		strings.HasPrefix(m, "image/png") ||
+		strings.HasPrefix(m, "image/gif") ||
+		strings.HasPrefix(m, "image/webp")
+}
+
+// ThumbnailKey returns the storage key for a file's thumbnail.
+func ThumbnailKey(fileID string) string {
+	return "thumbs/" + fileID + ".jpg"
+}
+
+// Generate reads an image from src, creates a thumbnail, and stores it.
+// Returns nil if generation succeeds, error otherwise.
+func Generate(ctx context.Context, st storage.Storage, fileID, mimeType string, src io.Reader) error {
+	if !SupportedMIME(mimeType) {
+		return fmt.Errorf("unsupported MIME type: %s", mimeType)
+	}
+
+	img, _, err := image.Decode(src)
+	if err != nil {
+		return fmt.Errorf("decode image: %w", err)
+	}
+
+	thumb := resize(img, maxWidth, maxHeight)
+
+	var buf bytes.Buffer
+	if err := jpeg.Encode(&buf, thumb, &jpeg.Options{Quality: 80}); err != nil {
+		return fmt.Errorf("encode thumbnail: %w", err)
+	}
+
+	key := ThumbnailKey(fileID)
+	if _, _, err := st.Put(ctx, key, &buf); err != nil {
+		return fmt.Errorf("store thumbnail: %w", err)
+	}
+	return nil
+}
+
+func resize(src image.Image, maxW, maxH int) image.Image {
+	bounds := src.Bounds()
+	w, h := bounds.Dx(), bounds.Dy()
+	if w == 0 || h == 0 {
+		return src
+	}
+
+	scaleW := float64(maxW) / float64(w)
+	scaleH := float64(maxH) / float64(h)
+	scale := scaleW
+	if scaleH < scale {
+		scale = scaleH
+	}
+	if scale >= 1 {
+		return src // already smaller than max
+	}
+
+	newW := int(float64(w) * scale)
+	newH := int(float64(h) * scale)
+	if newW < 1 {
+		newW = 1
+	}
+	if newH < 1 {
+		newH = 1
+	}
+
+	dst := image.NewRGBA(image.Rect(0, 0, newW, newH))
+	draw.BiLinear.Scale(dst, dst.Bounds(), src, src.Bounds(), draw.Over, nil)
+	return dst
+}