Make player character optional

Not every adventure needs to display a player character. Perhaps the adventure is considered to be in first-person view, or the player character is displyed in the each room as furniture (and the speech bubble is put next to it with npc_monologue instead of monologue).

Need to consider where/how the speech bubble (monologue) is displayed if the player character isn't there.

Start by tracing how the player character is rendered and how monologue and npc_monologue speech bubbles are positioned in each room. Define the behavior for adventures without a displayed player character, including where the speech bubble appears, then verify both first-person and furniture-style scenarios.

Written by the indexing model from the issue text.