feat: implement weapon set system (t_p2_weapons)

- WeaponData resource class with configurable weapon properties and
  pre-configured constants for rifle, pistol, shotgun, and SMG
- WeaponDefinitions singleton/static registry with WEAPONS dictionary
- WeaponServer node for server-authoritative weapon logic including
  fire rate cooldowns, ammo tracking, reload state machine, and
  multi-pellet hit-scan raycasting
- Extended WeaponManager with weapon inventory array, weapon switching,
  per-weapon state persistence, fire_animation_triggered signal

scripts/combat/weapon_definitions.gd

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+## WeaponDefinitions — Central registry of all weapon definitions.
+##
+## Provides a WEAPONS dictionary keyed by weapon_id for runtime lookup,
+## plus a convenience getter. The data itself lives in WeaponData constants,
+## so this file serves as a single import point for the full arsenal.
+##
+## Usage (as autoload singleton or direct preload):
+##   var data = WeaponDefinitions.get_weapon("rifle")
+##   # or:
+##   var all = WeaponDefinitions.WEAPONS
+##
+extends RefCounted
+class_name WeaponDefinitions
+
+# ---------------------------------------------------------------------------
+# Weapon Registry
+# ---------------------------------------------------------------------------
+
+## All weapons indexed by weapon_id — the single source of truth for the
+## game's starter arsenal. Add new weapons here and in WeaponData.
+const WEAPONS: Dictionary = {
+    "rifle":   WeaponData.RIFLE,
+    "pistol":  WeaponData.PISTOL,
+    "shotgun": WeaponData.SHOTGUN,
+    "smg":     WeaponData.SMG,
+}
+
+# ---------------------------------------------------------------------------
+# Lookup
+# ---------------------------------------------------------------------------
+
+## Return the WeaponData for the given weapon_id, or null if unknown.
+static func get_weapon(id: String) -> WeaponData:
+    return WEAPONS.get(id, null) as WeaponData