Complete librarian Stage 1: stale plans + MEMORY drift

Adds the last two deterministic Stage 1 checks and wires them into
scripts/librarian.sh:

- librarian_check_stale_plans.py: per docs/plans/*.md, uses
  `git log -1 --format=%cs` to get the last commit date and flags
  plans untouched in 60+ days. Plans should be either active or
  archived; long silence is drift.
- librarian_check_memory_drift.py: validates the user-memory dir
  (~/.claude/projects/<slug>/memory). Each MEMORY.md index line
  must point at a real file with frontmatter (name, description,
  type ∈ {user, feedback, project, reference}); no orphaned memory
  files. Memory dir is derived from repo root for portability.

Both run clean against current state.

Stage 1 declared complete. Promotable-archive and duplicate-prose
detection are moved to Stage 2 in the plan because both need LLM
judgment to avoid false positives — not pattern matching.

Next concrete step is the open Stage 1 finding from yesterday:
docs/performance.md at 914 lines, due for a split into sub-topic
notes.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

scripts/librarian_check_stale_plans.py

@@ -0,0 +1,77 @@
+"""Stale plan check for librarian Stage 1.
+
+Walks docs/plans/*.md (top-level only — archive subdir is separate)
+and flags plans whose last git commit is older than STALE_DAYS.
+Plans should be either actively worked on or archived (moved to
+docs/plans/archive/) — long-untouched files are usually drift.
+
+Usage:
+    uv run python scripts/librarian_check_stale_plans.py
+"""
+
+from __future__ import annotations
+
+import subprocess
+from datetime import datetime, timedelta
+from pathlib import Path
+
+STALE_DAYS = 60
+
+
+def _repo_root() -> Path:
+    current = Path(__file__).resolve()
+    for parent in current.parents:
+        if (parent / "pyproject.toml").is_file():
+            return parent
+    raise RuntimeError("pyproject.toml을 찾을 수 없어 repository root를 판정할 수 없습니다.")
+
+
+def _last_commit_date(root: Path, rel: Path) -> str | None:
+    result = subprocess.run(
+        ["git", "log", "-1", "--format=%cs", "--", str(rel)],
+        capture_output=True,
+        text=True,
+        cwd=root,
+        check=False,
+    )
+    out = result.stdout.strip()
+    return out if out else None
+
+
+def main() -> int:
+    root = _repo_root()
+    plans_dir = root / "docs" / "plans"
+    if not plans_dir.is_dir():
+        print("docs/plans not found; skipping stale-plan check.")
+        return 0
+
+    cutoff = (datetime.now() - timedelta(days=STALE_DAYS)).date()
+
+    stale: list[tuple[Path, str]] = []
+    for path in sorted(plans_dir.glob("*.md")):
+        rel = path.relative_to(root)
+        last = _last_commit_date(root, rel)
+        if last is None:
+            stale.append((rel, "untracked"))
+            continue
+        try:
+            last_date = datetime.strptime(last, "%Y-%m-%d").date()
+        except ValueError:
+            continue
+        if last_date < cutoff:
+            stale.append((rel, last))
+
+    if not stale:
+        print(f"No stale plans (all touched within {STALE_DAYS} days).")
+        return 0
+
+    print(f"Stale plan candidates (last commit > {STALE_DAYS} days ago):")
+    for rel, last in stale:
+        print(f"  {last}  {rel}")
+    print()
+    print("Action: archive (mv to docs/plans/archive/) or update if still active.")
+    return 1
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())