refactor: extract _assets.py and _utils.py from __init__.py (PR-2/8) (#2543)

* refactor: extract _assets.py and _utils.py from __init__.py

Move bundle path resolution and version lookup into _assets.py (stdlib only,
zero internal imports), and system utilities (subprocess, tool detection,
file operations) into _utils.py (imports only from ._console). Re-export all
moved symbols from __init__.py for backward compatibility. Update
test_check_tool.py to patch both specify_cli and specify_cli._utils namespaces
since constants are now defined in _utils.

* style: apply PR-1 review patterns to _assets.py and _utils.py

- Add module docstring to _assets.py (stdlib-only, zero internal imports)
- Add blank line after `from __future__ import annotations` in both files
- Replace `Optional[X]` with `X | None` throughout _utils.py (PEP 604)
- Remove unused `Optional` import from _utils.py
- Use explicit re-export form (`X as X`) for public symbols in __init__.py
- Remove unused `subprocess` and `tempfile` imports from __init__.py (moved to _utils.py)

src/specify_cli/_assets.py

@@ -0,0 +1,121 @@
+"""Bundle path resolution and version lookup for specify_cli.
+
+Stdlib-only; zero internal imports so it sits at the base of the dependency
+graph without risk of circular imports.
+"""
+from __future__ import annotations
+
+import importlib.metadata
+import re
+from pathlib import Path
+
+
+def _locate_core_pack() -> Path | None:
+    """Return the filesystem path to the bundled core_pack directory, or None.
+
+    Only present in wheel installs: hatchling's force-include copies
+    templates/, scripts/ etc. into specify_cli/core_pack/ at build time.
+
+    Source-checkout and editable installs do NOT have this directory.
+    Callers that need to work in both environments must check the repo-root
+    trees (templates/, scripts/) as a fallback when this returns None.
+    """
+    # Wheel install: core_pack is a sibling directory of this file
+    candidate = Path(__file__).parent / "core_pack"
+    if candidate.is_dir():
+        return candidate
+    return None
+
+
+def _repo_root() -> Path:
+    """Return the source checkout root used for editable installs."""
+    return Path(__file__).parent.parent.parent
+
+
+def _locate_bundled_extension(extension_id: str) -> Path | None:
+    """Return the path to a bundled extension, or None.
+
+    Checks the wheel's core_pack first, then falls back to the
+    source-checkout ``extensions/<id>/`` directory.
+    """
+    if not re.match(r'^[a-z0-9-]+$', extension_id):
+        return None
+
+    core = _locate_core_pack()
+    if core is not None:
+        candidate = core / "extensions" / extension_id
+        if (candidate / "extension.yml").is_file():
+            return candidate
+
+    # Source-checkout / editable install: look relative to repo root
+    candidate = _repo_root() / "extensions" / extension_id
+    if (candidate / "extension.yml").is_file():
+        return candidate
+
+    return None
+
+
+def _locate_bundled_workflow(workflow_id: str) -> Path | None:
+    """Return the path to a bundled workflow directory, or None.
+
+    Checks the wheel's core_pack first, then falls back to the
+    source-checkout ``workflows/<id>/`` directory.
+    """
+    if not re.match(r'^[a-z0-9](?:[a-z0-9-]*[a-z0-9])?$', workflow_id):
+        return None
+
+    core = _locate_core_pack()
+    if core is not None:
+        candidate = core / "workflows" / workflow_id
+        if (candidate / "workflow.yml").is_file():
+            return candidate
+
+    # Source-checkout / editable install: look relative to repo root
+    candidate = _repo_root() / "workflows" / workflow_id
+    if (candidate / "workflow.yml").is_file():
+        return candidate
+
+    return None
+
+
+def _locate_bundled_preset(preset_id: str) -> Path | None:
+    """Return the path to a bundled preset, or None.
+
+    Checks the wheel's core_pack first, then falls back to the
+    source-checkout ``presets/<id>/`` directory.
+    """
+    if not re.match(r'^[a-z0-9-]+$', preset_id):
+        return None
+
+    core = _locate_core_pack()
+    if core is not None:
+        candidate = core / "presets" / preset_id
+        if (candidate / "preset.yml").is_file():
+            return candidate
+
+    # Source-checkout / editable install: look relative to repo root
+    candidate = _repo_root() / "presets" / preset_id
+    if (candidate / "preset.yml").is_file():
+        return candidate
+
+    return None
+
+
+def get_speckit_version() -> str:
+    """Get current spec-kit version."""
+    try:
+        return importlib.metadata.version("specify-cli")
+    except Exception:
+        # Fallback: try reading from pyproject.toml
+        try:
+            import tomllib
+            pyproject_path = _repo_root() / "pyproject.toml"
+            if pyproject_path.exists():
+                with open(pyproject_path, "rb") as f:
+                    data = tomllib.load(f)
+                    return data.get("project", {}).get("version", "unknown")
+        except Exception:
+            # Intentionally ignore any errors while reading/parsing pyproject.toml.
+            # If this lookup fails for any reason, we fall back to returning "unknown" below.
+            pass
+    return "unknown"