docs: consistency pass across guides and readme

[jdwit]

A pass over the docs to bring them back in line with the current CLI surface (verified against the live typer reference output) and to clean up a few inconsistencies.

Changes

• playlists.md: renamed the Power moves section to Recipes; reframed the first example from a "watch later" curation (Watch Later is a special system playlist, not a search-curated one) to building a themed playlist; replaced the <new-banger> placeholder with <video-id>.
• README.md: fixed the CI badge, which pointed at jdwit/ytstudio instead of the actual jdwit/ytstudio-cli repo; dropped the "reply" claim from the comments feature line (there is no comments reply command; the surface is list/publish/reject/--ban). Also includes the earlier removal of the redundant "Power-user moves" block.
• analytics.md: corrected the Quota note. The previous text claimed analytics costs "1 unit per call against the Data API quota", but analytics runs against the separate YouTube Analytics API (its own query-cost quota), as already stated in api-quota.md.
• index.md: added Playlists to the homepage Highlights and the intro sentence; it shipped recently and was already in the nav and README features but missing here.
• videos.md: surfaced videos categories in the "List and inspect" block so the command is discoverable (it was only referenced inline in the sidecar section).

mkdocs build passes with no warnings of our own.