feat: move sbt to nft folder

[skywardboundd]

Closes #707

[github-actions]

To fix the formatting issues:

1. Install necessary dependencies: npm ci
2. Then, run this command:

npx remark -o --silent --silently-ignore standard/tokens/nft/sbt-how-it-works.mdx standard/tokens/overview.mdx standard/tokens/nft/comparison.mdx 

[github-actions]

Thanks for the update. I reviewed the docs changes touching token standards and references. There’s one item that needs a quick fix to keep internal anchors resolving correctly.

Findings (1)

High (1)

[HIGH] Broken internal anchor to “The scalable design: shard and prove”

Location: https://github.com/tact-lang/mintlify-ton-docs/blob/fff29977546ddf5edc0554bdbbc78ea0c518ab02/standard/tokens/nft/comparison.mdx?plain=1#L35-L35

Description:
The link to “airdrop markers” uses a percent-encoded colon in the anchor (#the-scalable-design%3A-shard-and-prove). The target heading on the airdrop page is “The scalable design: shard and prove,” whose generated slug removes punctuation, yielding #the-scalable-design-shard-and-prove (see standard/tokens/airdrop.mdx?plain=1#L23-L27). Per the style guide, internal anchors must resolve exactly.

Suggestion:
Update the anchor to the correct slug.

- ... [airdrop markers](/standard/tokens/airdrop#the-scalable-design%3A-shard-and-prove).
+ ... [airdrop markers](/standard/tokens/airdrop#the-scalable-design-shard-and-prove).

[skywardboundd]

Out of scope + it's normal ( we have link checks )

[github-actions]

Thanks for the updates to this PR. I reviewed the changes between main and pr_head and found no issues; no fixes are needed.

[anton-trunov]

@skywardboundd Please fix the merge conflicts