Is my main-panel's neutral currently bonded to ground?
The neutral and ground do not appear to be bonded

Take a closer look (and attach pictures for us) at the places I've circled in red below



On the right, it appears there's a green screw. According to the drawing, this makes sense, as it serves to bond the enclosure to the ground. It's marked on the drawings as "Bonded." It likely came from the factory like this.

On the left, there appears to be a hole for a bonding screw, but no screw is present. Accordingly, the drawing marks it as "Bond when required." To me, this indicates that the panel can be used as a main service panel when a screw is threaded through the hole in the lug and makes good electrical contact with the enclosure metal. Without this screw, the neutral and ground would be separate in this panel.

It also seems likely that they are not bonded because the there are no green or bare wires going to the left (neutral) busbar, and similarly, only green or bare wires seem to go to the right (ground) busbar.

Unrelated, but I am confused by the utter lack of ground wires anywhere, except the one going off into the knockout on the right and the large, twisted bundle. Do you know what kind of wiring you have in your house? Is everything in conduit or on metallic-clad cables? I'm just curious.