Fix wall-mounted ship wheels, command completions. Better error message when ship is too large. Fix some memory leaks and null config potential bugs.

• Add tab completion for /blockships subcommands with permission checks
• Add ship_wheel to give command
• Fix wall ship wheels using PLAYER_WALL_HEAD with correct facing
• Fix wall skull display transforms (Y offset, 180° yaw, Z offset)
• Report actual block count when ships exceed size limit (up to a point)
• Add safeBlockFace() helpers for null/invalid BlockFace parsing
• Fix memory leak in lastShulkerInteraction HashMap