chore: add version management and changelog

- Add pyproject.toml with project metadata and version (1.1.0)
- Update config.py to read version from pyproject.toml
- Update main.py to use centralized version in FastAPI app
- Add CHANGELOG.md documenting v1.0.0 and v1.1.0 changes

Version is now the single source of truth in pyproject.toml and is
displayed in the health check endpoint and API docs.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/config.py

@@ -4,9 +4,20 @@ Following best practices: modular settings, environment-based config.
 """
 
 from functools import lru_cache
+from pathlib import Path
 from pydantic import Field
 from pydantic_settings import BaseSettings, SettingsConfigDict
 
+# Read version from pyproject.toml
+try:
+    import tomllib
+    _pyproject_path = Path(__file__).parent.parent / "pyproject.toml"
+    with open(_pyproject_path, "rb") as f:
+        _pyproject = tomllib.load(f)
+    __version__ = _pyproject["project"]["version"]
+except Exception:
+    __version__ = "0.0.0"  # Fallback if pyproject.toml not found
+
 
 class Settings(BaseSettings):
     """Application settings loaded from environment variables."""
@@ -75,7 +86,7 @@ class Settings(BaseSettings):
 
     # Application
     app_name: str = Field(default="Library Desk", description="Application name")
-    app_version: str = Field(default="1.0.0", description="Application version")
+    app_version: str = Field(default=__version__, description="Application version")
     debug: bool = Field(default=False, description="Debug mode")
 
     @property