Derive __version__ from installed package metadata

Previously openkb/__init__.py had a hand-written __version__ = "0.1.0"
that drifted out of sync with pyproject.toml's version = "0.1.0.dev0",
and the chat REPL had a three-level try/except fallback to paper over
which string it would actually read. Make pyproject.toml the single
source of truth by having __init__.py pull its __version__ from the
installed package metadata via importlib.metadata, and simplify
_openkb_version in chat.py to just import __version__.

Author: rejojer

openkb/__init__.py

@@ -1 +1,7 @@
-__version__ = "0.1.0"
+"""OpenKB package."""
+from importlib.metadata import PackageNotFoundError, version as _version
+
+try:
+    __version__ = _version("openkb")
+except PackageNotFoundError:
+    __version__ = "0.0.0+unknown"

openkb/agent/chat.py

@@ -87,15 +87,8 @@ def _extract_preview(text: str, limit: int = 150) -> str:
 
 
 def _openkb_version() -> str:
-    try:
-        from importlib.metadata import version
-        return version("openkb")
-    except Exception:
-        try:
-            from openkb import __version__
-            return __version__
-        except Exception:
-            return ""
+    from openkb import __version__
+    return __version__
 
 
 def _display_kb_dir(kb_dir: Path) -> str: