rename python package projected_grpo -> vgrout

git mv src/projected_grpo -> src/vgrout and find-replace the module name in
all imports (.py), `-m projected_grpo.*` invocations (justfile), and the
[project] name (pyproject; setuptools auto-discovers via where=["src"]).

Left RESEARCH_JOURNAL.md untouched: its commands/paths are dated lab notes
tied to past commits, so rewriting them would falsify provenance. Repo dir,
git remote, and absolute paths unchanged.

Verified: `import vgrout` and `python -m vgrout.train --help` load the full
graph; verify_rewards.py + verify_gate_anchor.py (both import vgrout) pass.
Full `just smoke` is blocked upstream by missing gitignored data artifacts
(out/pools/{substrate,teacher_pool}, out/vhack/*smoke*), unrelated to the rename.

scripts/plot_substrate.py

@@ -39,7 +39,7 @@ import matplotlib.pyplot as plt
 import numpy as np
 from loguru import logger
 
-from projected_grpo.figs import save_fig
+from vgrout.figs import save_fig
 
 # hk_ column header -> (display mode, colour). Order = panel/legend order.
 # Colourblind-safe-ish qualitative set; one hue per loophole, reused across panels.