Per-sheep pen-time metrics, seed support, make webots → menu

* `controllers/shepherd_dog/shepherd_dog.py`
  - Tracks the first step at which each sheep crosses the gate; on
    auto-finish (all sheep penned) prints a `[results]` summary
    block: mode/drive/world/lidar/dogs/seed line, total simulated
    time, per-sheep penning order with absolute step + seconds since
    sim start, and the gate spread between the first and last
    penning.
  - Reads `HERDING_SEED` (env / runtime cfg) and seeds the
    controller's RNG when set. Empty = time-based default = old
    non-deterministic behaviour.
* `controllers/sheep/sheep.py` reads `HERDING_SEED` the same way
  (loading `herding_runtime.cfg` itself so it works even when
  Webots strips env vars) and seeds Python's RNG XOR'd with the
  sheep's name hash, so a fixed seed gives a reproducible flock
  trajectory without all sheep starting from identical wander state.
* `tools/run_webots.sh` writes `HERDING_SEED` into the runtime cfg
  (empty when unset so existing scripts keep their stochastic
  behaviour).
* `tools/webots_menu.sh` gains a Seed prompt (random / fixed
  integer); the launch summary box shows the choice next to the
  perception row.
* `Makefile`
  - `make webots`  now fires the interactive picker (replacing the
    old positional invocation).
  - `make webots_quick MODE=… DRIVE=… WORLD=… N=…` is the old
    positional path, kept for batch / scripted use.

Smoke-tested: menu renders Mode → Drive → World → LiDAR → Dogs
→ Sheep → Perception → Seed → Headless prompts and shows the
selected Seed value in the launch summary. 126 pytest cases still
pass.

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

Makefile

@@ -146,7 +146,7 @@ MODE             ?= rl
 
 
 .PHONY: all bc_demos bc rl rl_fast eval eval_fast eval_all eval_all_fast \
-        test webots webots_sweep clean clean_all help \
+        test webots webots_quick webots_sweep clean clean_all help \
         train_all train_diff_rect train_diff_round \
         train_mec_rect train_mec_round \
         train_all_fast train_diff_rect_fast train_diff_round_fast \
@@ -221,6 +221,9 @@ test:
 	$(PY) -m pytest tests/
 
 webots:
+	@bash tools/webots_menu.sh
+
+webots_quick:
 	tools/run_webots.sh $(N) $(MODE) $(DRIVE) $(WORLD)
 
 # Headless sweep across all modes × worlds × flock sizes.