feat(version): resolve the version from a generated module

A checkout carries no version of its own. The release stamps
hermes_cli/_version.py into the build tree, and a tree without it reports
0.0.0 rather than a number read out of git.

.gitignore

@@ -7,6 +7,8 @@
 /_pycache/
 *.pyc*
 __pycache__/
+# Generated by the release into the build tree; a checkout never carries one.
+hermes_cli/_version.py
 act/
 .act-sandbox-agent.*
 .venv/

hermes_cli/__init__.py

@@ -3,9 +3,15 @@
 import os
 import sys
 
-__version__ = "1.0.0"
 __release_date__ = "2026.9.21"
 
+# A checkout carries no version. The release stamps ``_version.py`` into the build
+# tree; without it the tree reports the placeholder, never a number read from git.
+try:
+    from hermes_cli._version import __version__  # type: ignore[import-not-found]
+except ImportError:
+    __version__ = "0.0.0"
+
 
 def _ensure_utf8():
     """Force UTF-8 stdout/stderr to prevent UnicodeEncodeError crashes.

tests/hermes_cli/test_version_resolution.py

@@ -0,0 +1,35 @@
+"""The shipped version comes from a generated module, never from the tree.
+
+A checkout carries no version of its own: the release stamps ``hermes_cli/_version.py``
+into the build tree, and a tree without that file reports the placeholder.
+"""
+import subprocess
+import sys
+from pathlib import Path
+
+REPO = Path(__file__).resolve().parents[2]
+
+
+def _version_of(tree: Path) -> str:
+    env = {"PYTHONPATH": str(tree)}
+    script = "import hermes_cli; print(hermes_cli.__version__)"
+    out = subprocess.run([sys.executable, "-c", script], cwd=tree, env=env,
+                         capture_output=True, text=True, check=True)
+    return out.stdout.strip()
+
+
+def test_generated_module_wins(tmp_path):
+    cli = tmp_path / "hermes_cli"
+    cli.mkdir()
+    (cli / "__init__.py").write_text((REPO / "hermes_cli" / "__init__.py").read_text())
+    (cli / "_version.py").write_text('__version__ = "0.21.5"\n')
+
+    assert _version_of(tmp_path) == "0.21.5"
+
+
+def test_absent_generated_module_is_the_placeholder(tmp_path):
+    cli = tmp_path / "hermes_cli"
+    cli.mkdir()
+    (cli / "__init__.py").write_text((REPO / "hermes_cli" / "__init__.py").read_text())
+
+    assert _version_of(tmp_path) == "0.0.0"