enable_kkbp()
Enable the Kitty keyboard protocol with progressive enhancement level 15
Pushes a KKBP stack entry and sets progressive enhancement flags to 15
(1 = disambiguate escape codes, 2 = report event types, 4 = report
alternate keys, 8 = report all keys as escape codes). Flag 16 (report
associated text) is intentionally excluded. The term.input module
assumes this exact enhancement level.