Add Threadlight world contact sheet

[RollNuts]

Summary

• Adds Threadlight world-contact-sheet assets and a 1280x800 gameplay mock.
• Records visual QA: v1 gameplay mock was too armored/monster-heavy; v2 moves the player toward field coat, apron, route sash, lantern-spool tool, and readable thread route control.
• Keeps Meshy/Maya spend blocked until route-tool or light-moth preview is justified by the gameplay rule.

Review Path

• Primary review image: docs/art/threadlight/threadlight-world-contact-sheet-v2.png
• Game-screen proof: docs/art/threadlight/threadlight-gameplay-mock-v2-1280x800.png
• Notes and prompt record: docs/art/threadlight/world-contact-sheet.md

Validation

• Visual inspection performed on gameplay mock, hub image, asset sheet, and final contact sheet.
• git diff --check passed.
• Local docs-gate equivalent passed.

Stack

Base PR: #18 (research/character-pipeline-and-video-tools)
Next PR should be a 30-second trailer beatboard, then only one low-cost 3D preview target: threadlight route tool or light-moth enemy.

[RollNuts]

Veripsa review note: this is a stacked art-direction PR on top of #18.

Scope: adds the first Threadlight world contact sheet and 1280x800 gameplay mock. The key review question is whether the world rule and commercial promise read from the screen: lantern-thread surveyor, route binding, light-moth/banner/knot threats, Loom Caravan hub.

Important QA: v1 gameplay mock skewed too armored and monster-heavy; v2 is the adopted version because it pushes field coat, apron, route sash, lantern-spool tool, and route-control read. Meshy/Maya spend remains blocked after this PR; next PR should be a trailer beatboard, then at most one low-cost preview target: route tool or light-moth.

[RollNuts]

Stack update for Veripsa: follow-up PR #20 is open on top of this branch: #20

Recommended order remains #18 -> #19 -> #20. #20 uses #19 assets only and turns the accepted world-contact-sheet into a 30-second trailer beatboard. No Meshy/Maya spend yet.