Update Dockerfile for PostgreSQL support

- Replace MySQL client with PostgreSQL client
- Use libpq-dev instead of libmysqlclient-dev
- Remove mysqlclient installation (using psycopg2-binary from requirements.txt)
- Install postgresql-client for pg_isready health checks

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

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

Dockerfile

@@ -3,17 +3,16 @@
 # ===================================================================
 FROM python:3.12-slim-bookworm AS builder
 
-# Install build dependencies for mysqlclient and other packages
+# Install build dependencies for PostgreSQL and other packages
 RUN apt-get update && apt-get install -y --no-install-recommends \
     gcc \
-    default-libmysqlclient-dev \
-    pkg-config \
+    libpq-dev \
     && rm -rf /var/lib/apt/lists/*
 
 # Install Python dependencies
 COPY requirements.txt /tmp/
 RUN pip install --user --no-cache-dir -r /tmp/requirements.txt \
-    && pip install --user --no-cache-dir mysqlclient gunicorn
+    && pip install --user --no-cache-dir gunicorn
 
 # ===================================================================
 # Stage 2: Runtime - Minimal production image
@@ -22,7 +21,7 @@ FROM python:3.12-slim-bookworm
 
 # Install runtime dependencies only
 RUN apt-get update && apt-get install -y --no-install-recommends \
-    default-mysql-client \
+    postgresql-client \
     curl \
     && rm -rf /var/lib/apt/lists/*