feat: add vision transfer backbones and IMF variants

experiment_suites/2026-04-05-rvistop-resnet-2cam/PLAN.md

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+# PLAN
+
+## Goal
+Train a 50k-step IMF baseline with the original ResNet vision backbone using r_vis + top as the only image conditioning.
+
+## Fixed comparison contract
+- same hyperparameters as the active top/front run
+- cameras: ['r_vis', 'top']
+- num_cams=2
+- head.cond_dim=144
+- host: 100.119.99.14
+- gpu: 2