simplify skill scripts: expose find_repo_root, fix split string, simplify label

- z3db.py: rename _find_repo_root to find_repo_root (make public) and
  add require_repo_root helper that exits on failure; update docstring
  and internal caller; fix unnecessary string literal split in log()
- memory_safety.py: remove 13-line duplicate find_repo_root function;
  import and use require_repo_root from z3db instead
- static_analysis.py: simplify two-line label assignment in
  print_findings to a single expression using 'or'

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

.github/skills/shared/z3db.py

@@ -3,7 +3,7 @@
 z3db: shared library and CLI for Z3 skill scripts.
 
 Library usage:
-    from z3db import Z3DB, find_z3, run_z3
+    from z3db import Z3DB, find_z3, run_z3, find_repo_root, require_repo_root
 
 CLI usage:
     python z3db.py init
@@ -131,7 +131,7 @@ class Z3DB:
         """Write to stderr and to the interaction_log table."""
         getattr(logger, level, logger.info)(message)
         self.conn.execute(
-            "INSERT INTO interaction_log (run_id, level, message) " "VALUES (?, ?, ?)",
+            "INSERT INTO interaction_log (run_id, level, message) VALUES (?, ?, ?)",
             (run_id, level, message),
         )
         self.conn.commit()
@@ -182,7 +182,7 @@ def find_z3(hint: str = None) -> str:
     if hint:
         candidates.append(hint)
 
-    repo_root = _find_repo_root()
+    repo_root = find_repo_root()
     if repo_root:
         for build_dir in ["build", "build/release", "build/debug"]:
             candidates.append(str(repo_root / build_dir / "z3"))
@@ -201,7 +201,8 @@ def find_z3(hint: str = None) -> str:
     sys.exit(1)
 
 
-def _find_repo_root() -> Optional[Path]:
+def find_repo_root() -> Optional[Path]:
+    """Walk up from cwd looking for the Z3 repository root."""
     d = Path.cwd()
     for _ in range(10):
         if (d / "CMakeLists.txt").exists() and (d / "src").is_dir():
@@ -213,6 +214,15 @@ def _find_repo_root() -> Optional[Path]:
     return None
 
 
+def require_repo_root() -> Path:
+    """Return the Z3 repo root, or exit with an error message if not found."""
+    root = find_repo_root()
+    if root is None:
+        logger.error("could not locate Z3 repository root")
+        sys.exit(1)
+    return root
+
+
 def run_z3(
     formula: str,
     z3_bin: str = None,