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

[ykns3]

Summary

• Opens the SkinCraft 3D button on inventory pages to stickers, patches, charms and agents
  alongside weapons/gloves. The embed protocol is inspect-based, so this is extension-side
  gating only — the item kind rides inside the masked inspect hex.
• Reads the masked hex from both layouts Steam ships: asset property 6 with a %propid:6%
  slot in the action link, or the hex embedded in the link itself. Accepts the inventory
  steam://run/730// and market steam://rungame/730/<id>/ forms. The launch link is rebuilt
  around the hex the viewer renders, so the two can't describe different items.
• Adds an inspect-requested embed event: the sandboxed iframe can't launch steam://, so it
  forwards the click and the extension launches the item on screen. No URL crosses the bridge —
  SkinCraftItem.inspectUrl is pattern-pinned at the page → content-script boundary and
  re-checked before navigation.

isAbstractType no longer dereferences asset.type unconditionally. This is shared code:
isCharm, isAgent, isSticker, isPatch, isCase, isMusicKit and isPin now match on
the tag branch where a description without type previously threw.

Merge order: the SkinCraft embed change must deploy first, or the new 3D tabs fail to load.

Validation

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

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Note

Medium Risk
Touches postMessage boundaries, window.location navigation to steam://, and shared item-type helpers; embed must deploy first or new tabs may fail to load.

Overview
Extends the SkinCraft 3D inventory viewer to stickers, patches, charms, and agents (not only weapons/gloves), with inspect hex read from asset property 6 and/or Steam’s masked Inspect in Game actions (%propid:6% or inline hex). Items now carry an optional inspectUrl (steam://…) rebuilt from the rendered hex and validated at the viewer protocol boundary.

Adds embed protocol event inspect-requested: the sandboxed iframe signals inspect clicks and the extension opens the pinned steam:// link for the currently loaded item (only after loaded, with STEAM_INSPECT_URL_PATTERN).

isAbstractType no longer assumes asset.type is always present (tag-based matching for half-hydrated Steam descriptions). Dev skincraft_embed_origin points at https://beta.skincraft.gg instead of localhost.

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