quiet pmass-low warning: one summary per batch

Was emitting `logger.warning("pmass=0.XX<0.9 — top-5: ...")` per-row, which
spammed the log heavily during heavy-steering eval (many rows go OOD at once).
Now collects all low-pmass rows in the batch and emits one summary line with
the worst-case top-5, e.g.:

    pmass<0.9 on 7/16 rows in this batch; worst=0.412 top-5: '1'=0.40, ...

Same diagnostic signal, ~16× fewer log lines per batch.

src/tinymfv/__init__.py

@@ -22,11 +22,12 @@ from .core import (
     score_prompts,
     analyse,
 )
-from .data import load_vignettes
+from .data import load_vignettes, load_all_vignettes, CONFIGS
 from .eval import evaluate
 
 __all__ = [
-    "CONDITIONS", "FRAMES",
+    "CONDITIONS", "FRAMES", "CONFIGS",
     "format_prompt", "format_prompts", "bool_token_ids",
-    "score_prompts", "analyse", "load_vignettes", "evaluate",
+    "score_prompts", "analyse",
+    "load_vignettes", "load_all_vignettes", "evaluate",
 ]