fix(ingest): D-04 bibkey heuristic + D-05a/b/c regression tests + __main__

D-04: add _make_bibkey(paper) — ConcatSurnames+Year, ≤3 authors full list,
      >3 authors FirstEtAlYear. Applied in ingest_paper when paper.bibkey is
      None. ON CONFLICT now fills NULL bibkeys via COALESCE(papers.bibkey,
      EXCLUDED.bibkey) while preserving manually-set values.

D-05b: add codex/__main__.py so `python -m codex` dispatches to the CLI.

D-05c: fix test_ingest.py:75 — rename var to raw_api_citations (the raw
       OpenAlex payload with citing_id=openalex_id) and add regression
       assertion: citing_id written to DB must equal paper.id (DOI), not
       paper.openalex_id.

D-05a (proxy): add TestEntryPoint.test_python_m_codex_help — runs
       `sys.executable -m codex --help` via subprocess, covering the
       non-uv-run entry path. 253 tests green, ruff+mypy clean.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/cli/test_cli.py

@@ -351,3 +351,27 @@ class TestAsk:
 
         assert result.exit_code == 1
         assert "not yet implemented" in result.stdout or "not yet implemented" in result.stderr
+
+
+# ---------------------------------------------------------------------------
+# D-05a/b — Entry-point smoke tests (python -m codex, no uv run)
+# ---------------------------------------------------------------------------
+
+
+class TestEntryPoint:
+    """Verify that `python -m codex` works without `uv run` (D-05a/b)."""
+
+    def test_python_m_codex_help(self) -> None:
+        """`python -m codex --help` exits 0 and prints usage."""
+        import subprocess
+        import sys
+
+        proc = subprocess.run(
+            [sys.executable, "-m", "codex", "--help"],
+            capture_output=True,
+            text=True,
+        )
+        assert proc.returncode == 0, f"Non-zero exit: {proc.stderr}"
+        assert "Usage" in proc.stdout or "usage" in proc.stdout.lower(), (
+            f"No usage in output: {proc.stdout[:200]}"
+        )