Meta made $196 billion last year selling ads. That's 97.6% of everything it earns. This weekend it's the one buying airtime, putting its new agent Muse on national TV during the football slate. Looks backwards until you run the math on Meta's own inventory. Every slot in Instagram or Facebook clears at auction, and Meta's average price per ad rose 12% last quarter. A house ad for Muse means forfeiting the winning bid on that impression. Promoting Muse to its own 3.6 billion daily users would…