Report the real package version instead of hardcoded 0.1.0

`pygit --version`, `pygit diagnose`, and `pygit bugreport` all printed a
hardcoded "0.1.0" regardless of the installed version. Derive __version__ from
the installed distribution metadata (single source of truth = pyproject), with
a "0+unknown" fallback for unbuilt source trees, and use it at all three sites.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: blhsing

pythongit/__init__.py

@@ -2,4 +2,20 @@
 from .repo import Repository
 
 __all__ = ["Repository"]
-__version__ = "0.1.0"
+
+
+def _resolve_version() -> str:
+    """Single source of truth: the installed distribution's version (from
+    pyproject), falling back to a literal when running from an unbuilt source
+    tree where no distribution metadata is present."""
+    try:
+        from importlib.metadata import PackageNotFoundError, version
+        try:
+            return version("pure-python-git")
+        except PackageNotFoundError:
+            return "0+unknown"
+    except Exception:
+        return "0+unknown"
+
+
+__version__ = _resolve_version()

pythongit/cli.py

@@ -4879,7 +4879,8 @@ def cmd_diagnose(argv: list[str]) -> int:
     args = ap.parse_args(argv)
     repo = _repo()
     lines = []
-    lines.append(f"pythongit version: 0.1.0")
+    from . import __version__ as _ppg_version
+    lines.append(f"pythongit version: {_ppg_version}")
     lines.append(f"gitdir: {repo.gitdir}")
     lines.append(f"worktree: {repo.path}")
     lines.append(f"branches: {len(refs_mod.list_branches(repo))}")
@@ -4903,8 +4904,9 @@ def cmd_bugreport(argv: list[str]) -> int:
     ap.add_argument("-o", "--output-directory", default=None)
     args = ap.parse_args(argv)
     import platform
+    from . import __version__ as _ppg_version
     lines = []
-    lines.append(f"pythongit: 0.1.0")
+    lines.append(f"pythongit: {_ppg_version}")
     lines.append(f"python: {platform.python_version()}")
     lines.append(f"platform: {platform.platform()}")
     try: