[CloudeaSoft]

Summary

Fix handheld weapons using the observing client's cursor, spawning duplicate projectiles in multiplayer, and rendering incorrectly under inverted gravity.

• Rename HandholdProjectile to HandheldProjectile and migrate all implementations.
• Use the owner's synchronized cursor and initialize received projectiles without relying on OnSpawn.
• Restrict projectile creation to the owning client while preserving sounds and visual effects on other clients.
• Apply gravity-aware arm offsets and sprite orientation; synchronize laser crystal parent references and calculate laser endpoints outside rendering.
• Remove redundant overrides and assignments, and correct three weapon rarity assignments to Item.rare.

Fixes #367.

Validation

• dotnet build /p:WarningLevel=0 — passed.
• dotnet test /p:WarningLevel=0 /p:NotCopyLocal=false — 541 tests passed, including 11 new regression tests.
• UTF-8 BOM and diff whitespace checks — passed.

The test invocation enables dependency copying to avoid the existing FontStashSharp.FNA test discovery issue. No build configuration files were changed.

In-game multiplayer, dedicated-server behavior, inverted-gravity visuals, and audio still require manual verification.