feat(experiment): behavioral convergence exp 1 -- cross-session affective memory

First entry in behavioral_convergence_practice.md: three SEM entities
(rusty sword, healing potion, poison potion) across two sessions.
11/11 hypotheses confirmed. Key finding: shared potion concept carries
mixed valence from both healing and poison interactions.

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

Author: dennys246