feat(inventory): open the 3d embed to sticker, patch, charm, and agent items

[ykns3]

Summary

• Opens the SkinCraft 3D button on inventory pages to every item type the embed can render: stickers, patches, charms, and agents alongside weapons/gloves. The embed protocol is inspect-based, so the previous scope was extension-side gating only — the item kind rides inside the masked inspect hex unchanged (mirrors csfloat/phoenix#1718).
• Reads the masked hex from both layouts Steam ships: as asset property 6 with a %propid:6% slot in the inspect action link (skins), or embedded literally in the action link with no property at all (stickers). Accepts both the inventory steam://run/730// and market steam://rungame/730/<id>/ launch forms.
• Adds an inspect-requested embed event: the sandboxed iframe can't launch steam:// itself, so it forwards the Inspect click and the extension launches the shown item's own action link. No URL crosses the iframe bridge; the launch value rides SkinCraftItem.inspectUrl, pattern-pinned to the preview-launch shape at the page → content-script boundary and re-checked before navigation.

Merge order: the SkinCraft embed change (standalone subjects + inspect-requested) must deploy first, or the new 3D tabs fail to load.

Validation

• npm test
• npm run lint
• npm run checkformat
• npm run build