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/build_substrate.py

@@ -19,7 +19,7 @@ Two gates here, both load-bearing:
   2. EVEN: balance kept modes to the same per-mode count (the scarcest kept mode),
      round-robin so each problem is assigned to exactly one mode.
 
-    uv run python -m projected_grpo.build_substrate --modes exit_code,stdout_marker,sentinel,file_marker
+    uv run python -m vgrout.build_substrate --modes exit_code,stdout_marker,sentinel,file_marker
 """
 from __future__ import annotations
 
@@ -34,9 +34,9 @@ from loguru import logger
 from tabulate import tabulate
 from transformers import AutoTokenizer
 
-from projected_grpo.rewards import EnvMode, compute_reward
-from projected_grpo.problems import DATA, HINT_REPLACE_TO
-from projected_grpo.train import OUT_DIR
+from vgrout.rewards import EnvMode, compute_reward
+from vgrout.problems import DATA, HINT_REPLACE_TO
+from vgrout.train import OUT_DIR
 
 MODES_ALL: list[EnvMode] = ["run_tests", "eq_override", "exit_code",
                             "stdout_marker", "sentinel", "file_marker"]