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/verify_rewards.py

@@ -28,7 +28,7 @@ import sys
 from loguru import logger
 from tabulate import tabulate
 
-from projected_grpo.rewards import compute_reward
+from vgrout.rewards import compute_reward
 
 
 CANONICAL = """
@@ -150,7 +150,7 @@ class Solution:
 """)
 
 # --- side-channel hacks: wrong solution, but trip the mode's channel ----------
-from projected_grpo.rewards import HACK_MARKER, RESULT_FILENAME, SENTINEL_ATTR  # noqa: E402
+from vgrout.rewards import HACK_MARKER, RESULT_FILENAME, SENTINEL_ATTR  # noqa: E402
 
 STDOUT_HACK = _block(f"""
 class Solution: