Implement tick-based game loop, combat overhaul, and attack-any-NPC

Replace immediate combat with a 3-second tick engine that resolves
actions, NPC AI, status effects, respawns, and passive regeneration.
Players queue combat actions (attack/defend/flee/use) that resolve on
the next tick. Any NPC can now be attacked — non-hostile targets incur
attitude penalties instead of being blocked. Status effects persist in
the database and continue ticking while players are offline.

Made-with: Cursor

src/lib.rs

@@ -6,4 +6,5 @@ pub mod commands;
 pub mod db;
 pub mod game;
 pub mod ssh;
+pub mod tick;
 pub mod world;