chore: pin all Python dependency versions (#82)

Pin all requirements.txt deps to exact versions sourced from production
container. Move pytest/pytest-asyncio to new requirements-dev.txt. Pin
Dockerfile base image from python:3.12-slim to python:3.12.13-slim.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Dockerfile

@@ -1,4 +1,4 @@
-FROM python:3.12-slim
+FROM python:3.12.13-slim
 
 WORKDIR /usr/src/app
 

requirements-dev.txt

@@ -0,0 +1,3 @@
+-r requirements.txt
+pytest==9.0.2
+pytest-asyncio==1.3.0

requirements.txt

@@ -1,15 +1,13 @@
-discord.py
-pygsheets
-pydantic
-gsheets
-bs4
-peewee
-sqlmodel
-alembic
-pytest
-pytest-asyncio
-numpy<2
-pandas
-psycopg2-binary
-aiohttp
+discord.py==2.7.1
+pygsheets==2.0.6
+pydantic==2.12.5
+gsheets==0.6.1
+bs4==0.0.2
+peewee==4.0.1
+sqlmodel==0.0.37
+alembic==1.18.4
+numpy==1.26.4
+pandas==3.0.1
+psycopg2-binary==2.9.11
+aiohttp==3.13.3
 # psycopg[binary]