v8.0 Phase 1: PR openai#549 baseline + TTT enabled (2 lines changed)

Run 0: PR openai#549 UNMODIFIED (merged SOTA 1.1194, verified 3-seed)
Run 1: PR openai#549 + TTT_ENABLED=1 + TTT_LR=0.0005 (2 lines changed)

Both have FA3→FA2→SDPA fallback for non-Hopper GPUs.
Following retro: one change per run, baseline first.

Expected: Run 1 should achieve ~1.094-1.104 (beats 1.1144 target).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: sunnypatneedi