Add package structure and resource path utilities

- Created langbot/ package with __init__.py and __main__.py entry point
- Added paths utility to find frontend and resource files from package installation
- Updated config loading to use resource paths
- Updated frontend serving to use resource paths
- Added MANIFEST.in for package data inclusion
- Updated pyproject.toml with build system and entry points

Co-authored-by: RockChinQ <45992437+RockChinQ@users.noreply.github.com>

pyproject.toml

@@ -99,6 +99,24 @@ Homepage = "https://langbot.app"
 Documentation = "https://docs.langbot.app"
 Repository = "https://github.com/langbot-app/LangBot"
 
+[project.scripts]
+langbot = "langbot.__main__:main"
+
+[build-system]
+requires = ["setuptools>=61.0", "wheel"]
+build-backend = "setuptools.build_meta"
+
+[tool.setuptools]
+packages = { find = {} }
+include-package-data = true
+
+[tool.setuptools.package-data]
+"*" = [
+    "web/out/**/*",
+    "templates/**/*",
+    "res/**/*",
+]
+
 [dependency-groups]
 dev = [
     "pre-commit>=4.2.0",