Update deps (fastapi, pych-client, pydantic-settings), migrate poetry dev groups, fix Dockerfile (#14)

- Upgrade fastapi from ^0.81.0 → ^0.116.2 (brings in starlette >=0.47.2)
- Upgrade pych-client from ^0.3.1 → ^0.4.1
- Add pydantic-settings ^2.10.1 and update BaseSettings import
  (BaseSettings was removed from pydantic v2 and moved to the standalone
  pydantic-settings package)
- Keep anyio <4 for httpx compatibility
- Migrate [tool.poetry.dev-dependencies] → [tool.poetry.group.dev.dependencies]
- Dockerfile: replace poetry install --no-root --no-dev with --without dev
   (the --no-dev flag was removed in Poetry ≥1.2 in favor of dependency groups)
- Regenerated poetry.lock by running poetry update on a test GCP VM with:
   - Ubuntu 24.04.3 LTS
   - Poetry 1.8.2
   - Python 3.12.3
This resolves GitHub Dependabot alerts and ensures dependency consistency.

Author: Elenetta17

Dockerfile

@@ -9,7 +9,7 @@ RUN poetry config virtualenvs.in-project true
 COPY pyproject.toml pyproject.toml
 COPY poetry.lock poetry.lock
 
-RUN poetry install --no-root --no-dev \
+RUN poetry install --no-root --without dev \
     && rm -rf /root/.cache/*
 
 COPY guesthouse guesthouse

guesthouse/settings.py

@@ -1,6 +1,6 @@
 from pathlib import Path
 
-from pydantic import BaseSettings
+from pydantic_settings import BaseSettings
 
 
 class Settings(BaseSettings):