Adaptive sync doc

[evanorti]

New doc for adaptive sync feature

[greptile-apps]

Greptile Summary

This PR adds a new documentation page for the experimental adaptive sync feature in CometBFT, which allows a node to participate in consensus while still catching up via blocksync. The page is well-structured and covers the use case, internal mechanics, and configuration clearly. A minor unannounced side-effect in docs.json also registers the pre-existing lib-p2p experimental doc into the navigation for the first time.

• New adaptive-sync.mdx page documents the feature's purpose, behaviour differences (peer polling interval, transient peer timeouts, mempool acceptance, block deduplication), and how to enable it via config.toml.
• docs.json correctly wires adaptive-sync into the Experimental navigation group.
• lib-p2p is also silently added to the navigation in the same docs.json change — worth confirming this is intentional.
• Minor: two consecutive blank lines appear between the config code block and the closing paragraph in adaptive-sync.mdx.

Confidence Score: 5/5

• Safe to merge after confirming the lib-p2p navigation addition is intentional.
• The changes are purely documentation. The new MDX page is accurate, well-written, and links to an existing file. Both referenced files exist on disk, so there is no risk of broken navigation links. The only items worth addressing are a minor formatting nit and a question about the unannounced lib-p2p entry.
• No files require special attention beyond confirming the lib-p2p navigation registration in docs.json.

Important Files Changed

Filename	Overview
cometbft/next/docs/experimental/adaptive-sync.mdx	New documentation page for the adaptive sync experimental feature. Content is clear and accurate. Minor: double blank line between the config code block and the closing paragraph.
docs.json	Adds both adaptive-sync and lib-p2p to the Experimental navigation group. The lib-p2p addition is undocumented in the PR description; both target files exist on disk so no broken-link risk.

_{Last reviewed commit: "Create adaptive-sync..."}