riddle takeover mode: SDK-linked quill backend (instant ink) + fast pi oracle (openai-codex/gpt-5.5, reasoning off, inline image)

- build-takeover.sh links via ferrari SDK gcc to resolve GLIBC 2.36/2.38 syms
- oracle.rs: pi with openai-codex gpt-5.5 --thinking off, @inline image (no tool call), ~5-7s
- riddle-takeover.sh: stop xochitl, run against vendor engine, always restore