Drop versioning vocabulary, polish docstrings, fix world-aware policy resolution

User-facing pass after the project was decided to be a single
submission with no inner iterations.

* Remove every "v1"/"v2"/"versioning" reference from the docs:
  - README mecanum section trims the "v1 predates the rewrite" prose
    in favour of a self-contained retrain recipe.
  - The 3.2 GB `training/runs/v1_clean/` backup directory is deleted.
* Refresh control-layer docstrings:
  - `sheep_tracker.py` header now describes the three actual pipeline
    stages (consensus, prediction, pen latching) instead of layering
    the consensus stage on top of a stale "predictive mode" preamble.
  - `controllers/shepherd_dog/shepherd_dog.py` mode list is
    up-to-date — adds `universal`, removes outdated single-policy
    default paths, mentions `HERDING_USE_GT=1` as the perception
    ablation.
* Refresh training command examples:
  - `training/bc/collect.py` and `training/bc/pretrain.py` usage
    snippets show the world-suffixed paths the Makefile actually
    uses; the `--out` arg is now required so old "demos.npz"
    invocations error loudly instead of silently overwriting.
  - `training/README.md` rewritten — drops the legacy `runs/bc`
    diagram, documents the per-(drive, world) pipeline, and adds
    the mecanum retraining caveat.
* Fix policy-directory resolution end-to-end:
  - `tools/run_webots.sh` now tries
    `training/runs/{bc,rl}_<drive>_<world>` first, then the drive-
    only path, then the bare-mode legacy path — matching the actual
    on-disk layout. Previously it looked for `bc_<drive>` (no
    world) and silently fell back to `bc`, masking the world
    selection.
  - `controllers/shepherd_dog/shepherd_dog.py:_resolve_policy_dir`
    has the same fix plus a latent NameError unmasked: it referenced
    `DRIVE_MODE` before that variable was set at module load. The
    block is restructured so MODE/DRIVE_MODE/WORLD are resolved
    first, then the function uses them as explicit arguments.

126 pytest cases still pass.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

tools/run_webots.sh

@@ -60,19 +60,26 @@ DST="$ROOT/worlds/${WORLD}_test.wbt"
 if [[ -n "${HERDING_POLICY_DIR:-}" ]]; then
     RESOLVED_POLICY_DIR="$HERDING_POLICY_DIR"
 else
-    # Try drive-mode-specific path first, then legacy path.
+    # The training pipeline writes policies to:
+    #   training/runs/{bc,rl}_<drive>_<world>
+    # Try that first; fall back to the drive-only and finally the
+    # bare-mode legacy paths so older policy checkouts still load.
     if [[ "$MODE" == "rl" ]]; then
-        DRIVED="$ROOT/training/runs/rl_${DRIVE}"
-        LEGACY="$ROOT/training/runs/rl"
+        BASE="rl"
     else
-        DRIVED="$ROOT/training/runs/bc_${DRIVE}"
-        LEGACY="$ROOT/training/runs/bc"
-    fi
-    if [[ -d "$DRIVED" ]]; then
-        RESOLVED_POLICY_DIR="$DRIVED"
-    else
-        RESOLVED_POLICY_DIR="$LEGACY"
+        BASE="bc"
     fi
+    for CAND in \
+        "$ROOT/training/runs/${BASE}_${DRIVE}_${WORLD}" \
+        "$ROOT/training/runs/${BASE}_${DRIVE}" \
+        "$ROOT/training/runs/${BASE}"
+    do
+        if [[ -d "$CAND" ]]; then
+            RESOLVED_POLICY_DIR="$CAND"
+            break
+        fi
+    done
+    : "${RESOLVED_POLICY_DIR:=$ROOT/training/runs/${BASE}_${DRIVE}_${WORLD}}"
 fi
 
 cp "$SRC" "$DST"