feat: add devcontainer configuration and installation script

Add a devcontainer configuration to streamline the development 
environment setup. Introduce an `install.sh` script to install 
the project in editable mode. Update the Dockerfile to use 
the `python:3.13-slim-bullseye` base image and install 
dependencies using `apt-get` for better compatibility.

Dockerfile

@@ -1,9 +1,11 @@
-FROM python:3.13-alpine
+FROM python:3.13-slim-bullseye
 
 USER root
 
 # Runtime dependency
-RUN apk add --no-cache ffmpeg
+RUN apt-get update && apt-get install -y --no-install-recommends \
+    ffmpeg \
+ && rm -rf /var/lib/apt/lists/*
 
 RUN pip install markitdown