Real-image posters: scale to the box's pixel size

Ghostty shows an image smaller than its placement at its own size, so
library posters (Radarr's poster-500 is 333x500, not 500x750) came out
smaller than the 426x640 remote ones. Images are now scaled (bilinear)
to exactly cols*cellWidth x rows*cellHeight pixels before upload, and
library titles use the original poster for real images. The disk cache
stores posters as decoded (JPEG) instead of the possibly large originals.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/ui/kitty.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"encoding/base64"
 	"fmt"
+	xdraw "golang.org/x/image/draw"
 	"image"
 	"image/png"
 	"strings"
@@ -43,6 +44,11 @@ type kittyGraphics struct {
 
 	holdUntil time.Time    // no real images until then (the window is being resized)
 	debug     func(string) // reports what is uploaded, if set
+	// cellPixels returns the size of a cell in pixels (0 if unknown): images are
+	// scaled to exactly fill their cells, because terminals do not all enlarge
+	// an image that is smaller than its placement (Ghostty shows it at its own
+	// size, so a small poster came out smaller than the others).
+	cellPixels func() (w, h int)
 }
 
 // settleDelay is how long the window size must stay the same before real
@@ -92,9 +98,15 @@ func (k *kittyGraphics) show(img *image.RGBA, rect image.Rectangle, cols, rows i
 	if id, ok := k.ids[key]; ok {
 		return id, nil
 	}
+	var src image.Image = img.SubImage(rect)
+	if k.cellPixels != nil {
+		if cw, ch := k.cellPixels(); cw > 0 && ch > 0 {
+			src = scaleImage(src, cols*cw, rows*ch)
+		}
+	}
 	var data bytes.Buffer
 	enc := png.Encoder{CompressionLevel: png.BestSpeed}
-	if err := enc.Encode(&data, img.SubImage(rect)); err != nil {
+	if err := enc.Encode(&data, src); err != nil {
 		return 0, err
 	}
 	encoded := base64.StdEncoding.EncodeToString(data.Bytes())
@@ -130,7 +142,8 @@ func (k *kittyGraphics) show(img *image.RGBA, rect image.Rectangle, cols, rows i
 	k.ids[key] = id
 	k.latest[img] = key
 	if k.debug != nil {
-		k.debug(fmt.Sprintf("graphics: id %d, poster %dx%d px cropped to %v, placed over %dx%d cells", id, img.Bounds().Dx(), img.Bounds().Dy(), rect, cols, rows))
+		k.debug(fmt.Sprintf("graphics: id %d, poster %dx%d px cropped to %v, sent as %dx%d px, placed over %dx%d cells",
+			id, img.Bounds().Dx(), img.Bounds().Dy(), rect, src.Bounds().Dx(), src.Bounds().Dy(), cols, rows))
 	}
 	return id, nil
 }
@@ -175,3 +188,15 @@ func kittyTerminal(env func(string) string) bool {
 	}
 	return false
 }
+
+// scaleImage resizes src to w×h pixels, smoothly (bilinear) both up and down.
+// Sizes beyond 4000 pixels are not made (a misreported cell size).
+func scaleImage(src image.Image, w, h int) image.Image {
+	b := src.Bounds()
+	if w <= 0 || h <= 0 || w > 4000 || h > 4000 || (w == b.Dx() && h == b.Dy()) {
+		return src
+	}
+	dst := image.NewRGBA(image.Rect(0, 0, w, h))
+	xdraw.BiLinear.Scale(dst, dst.Bounds(), src, b, xdraw.Src, nil)
+	return dst
+}