examples(port_datasets): generalize RoboCasa builder + add smoke script

- Add ATOMIC_TASKS, COMPOSITE_UNSEEN_TASKS and four new --task-set keys
  (atomic, composite_unseen, composite_all, composite_atomic) so the same
  builder produces the 50-task target benchmark or the 300-task Human300
  pretraining slice (via --split=pretrain --task-set=all) without
  duplicating logic.
- Stop hardcoding the composite_seen tag on the HF push; tags are now
  derived from --split / --source / --task-set so atomic, composite_all,
  and pretrain runs land with accurate metadata.
- Refresh module docstring to match the broader scope.
- Add scripts/build_robocasa_smoke.sh: 2-atomic-task smoke dataset
  (~1k episodes, ~131k frames) for fast end-to-end training validation
  before kicking off Human300-scale runs.

scripts/build_robocasa_smoke.sh

@@ -0,0 +1,47 @@
+#!/bin/bash
+# Build a tiny RoboCasa smoke dataset (2 short atomic tasks, all episodes) for
+# fast end-to-end training validation before the real run.
+#
+# Defaults: target/human, OpenStandMixerHead + NavigateKitchen (~1k episodes,
+# ~131k frames, ~109 min @ 20 fps), 2 SLURM workers on hopper-cpu.
+#
+# Override via env: TASKS, REPO_ID, WORK_DIR, WORKERS, CPUS, PARTITION, LOCAL=1.
+
+set -euo pipefail
+
+cd "${LEROBOT_ROOT:-$HOME/lerobot}"
+source ~/miniconda3/etc/profile.d/conda.sh
+conda activate lerobot
+
+REPO_ID="${REPO_ID:-${HF_USER:?HF_USER is unset}/robocasa_smoke_2atomic_v3}"
+WORK_DIR="${WORK_DIR:-/fsx/${USER}/robocasa/datasets/v1.0}"
+ROBOCASA_ROOT="${ROBOCASA_ROOT:-/fsx/${USER}/robocasa}"
+LOGS_DIR="${LOGS_DIR:-/fsx/${USER}/logs/robocasa}"
+TASKS="${TASKS:-OpenStandMixerHead NavigateKitchen}"
+WORKERS="${WORKERS:-2}"
+CPUS="${CPUS:-8}"
+PARTITION="${PARTITION:-hopper-cpu}"
+LOCAL="${LOCAL:-0}"
+
+ARGS=(
+    examples/port_datasets/slurm_build_robocasa_composite_seen.py
+    --repo-id="$REPO_ID"
+    --work-dir="$WORK_DIR"
+    --robocasa-root="$ROBOCASA_ROOT"
+    --split=target --source=human
+    --tasks $TASKS
+    --workers="$WORKERS"
+    --cpus-per-task="$CPUS"
+    --partition="$PARTITION"
+    --mem-per-cpu=4G
+    --time=04:00:00
+    --logs-dir="$LOGS_DIR"
+    --job-name=port_robocasa_smoke
+)
+if [[ "$LOCAL" == "1" ]]; then
+    ARGS+=(--slurm=0)
+fi
+
+echo "Smoke dataset: $REPO_ID"
+echo "Tasks: $TASKS"
+python "${ARGS[@]}"