Shotgun QoL – allow firing during shell-by-shell reload (CS-style)

Summary:
Please allow shotguns that reload shell-by-shell to fire as soon as the first shell is chambered, instead of locking the player until the reload finishes.

Rationale (Balance & UX):
• Increases skill expression and meaningful risk/reward (cancel reload vs. finish).  
• Reduces frustration in close-quarters without boosting overall DPS.  
• Mirrors proven behavior from competitive shooters like CS2.

Proposal:
• After inserting the first shell, enable firing after ~120–180 ms (tunable for balancing issues).  
• Add a small spread/raise penalty on interrupt.  
• Prevent animation-cancel exploits with a brief lockout (~200 ms) before resuming reload.

Validation:
Measure TTK impact in 0–10 m, check for abuse with weapon-switch cancels, ensure parity across pump/auto shotguns.