Qendering v0.13.0

v0.13.0: weapon render mode with bone-snapped attachments

New Weapons mode: pick a weapon (.ydr/.yft), tick the attachment models
beside it (scope, suppressor, flashlight, mag), and render one assembled
still. Attachments snap onto the weapon's WAP* skeleton bones so they land
correctly. Weapon palette shaders that reference an unshipped tint texture
are repointed at the real diffuse to avoid magenta renders. Screenshot of
the mode added at docs/weapons.png (shown in the README).