2.2.0-rc2

[yagop]

Release 2.2.0-rc2 with the reply-tracking size budget rename (maxEntriesPerChat and maxBytesPerChat), core and CI maintenance, and the v2 migration documentation cleanup.

Updates package.json and moves the unreleased notes into the dated changelog entry. This prerelease will publish under npm's next tag.

• npm run check is clean, including all 249 unit tests
• npm run build is clean
• Generated sources are unchanged; npm run generate:docs produces no diff

References: #1363, #1364, #1365, #1366