harness: rasterize SVG icon to PNG for Forgejo avatar upload (fixes #197)

nix/templates/harness-base.nix

@@ -431,7 +431,7 @@
       path = [
         pkgs.curl
         pkgs.coreutils
-        pkgs.python3
+        pkgs.librsvg
       ];
       script = ''
         ICON=/etc/hyperhive/icon.svg
@@ -452,9 +452,16 @@
           exit 0
         fi
         TOKEN=$(cat "$TOKEN_FILE")
-        # Base64-encode the SVG and wrap in a data URI.
-        IMAGE=$(base64 -w 0 < "$ICON")
-        DATA_URI="data:image/svg+xml;base64,$IMAGE"
+        # Rasterize SVG → PNG (Forgejo's Go image library can't decode SVG).
+        PNG=$(mktemp --suffix=.png)
+        if ! rsvg-convert -f png -w 256 -h 256 "$ICON" -o "$PNG" 2>/dev/null; then
+          echo "forge-avatar-sync: rsvg-convert failed; skipping"
+          rm -f "$PNG"
+          exit 0
+        fi
+        IMAGE=$(base64 -w 0 < "$PNG")
+        rm -f "$PNG"
+        DATA_URI="data:image/png;base64,$IMAGE"
         RESP=$(curl -sf --max-time 10 \
           -X POST "$FORGE_URL/api/v1/user/avatar" \
           -H "Authorization: token $TOKEN" \