fix: use absolute paths for database to ensure persistence

Critical bug fix: Path(__file__).parent.parent returns a relative path,
causing the database to be created in different locations depending on
the working directory. This caused data loss on container restarts.

Changes:
- Add .resolve() to BASE_DIR in src/config.py and migrations/env.py
- Fix admin dashboard showing 0 for participant count (was hardcoded)
- Fix exchange detail page to show actual participant list
- Add startup diagnostics to entrypoint.sh for troubleshooting

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

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

entrypoint.sh

@@ -4,6 +4,22 @@ set -e  # Exit on any error
 # Ensure data directory exists
 mkdir -p /app/data
 
+echo "=== Sneaky Klaus Container Startup ==="
+echo "Data directory: /app/data"
+echo "Database path: /app/data/sneaky-klaus.db"
+
+# Check if database exists
+if [ -f /app/data/sneaky-klaus.db ]; then
+    echo "Existing database found ($(ls -lh /app/data/sneaky-klaus.db | awk '{print $5}'))"
+else
+    echo "No existing database - will be created by migrations"
+fi
+
+# List contents of data directory
+echo "Data directory contents:"
+ls -la /app/data/ || echo "(empty)"
+
+echo ""
 echo "Running database migrations..."
 if uv run alembic upgrade head; then
     echo "Database migrations completed successfully"
@@ -13,5 +29,6 @@ else
     exit 1
 fi
 
+echo ""
 echo "Starting application server..."
 exec gunicorn --bind 0.0.0.0:8000 --workers 2 --threads 4 main:app