Fix integration test data directory permissions

Root cause: Pulse server was crashing on startup with permission denied when
trying to create .encryption.key file.

The docker-compose test config set PULSE_DATA_DIR=/tmp/pulse-test-data, but
this directory was owned by root (created by Docker volume mount). The
entrypoint script only chowns /data, not /tmp/pulse-test-data.

Solution: Change PULSE_DATA_DIR to /data which is already handled by the
entrypoint script's chown command (line 36 of docker-entrypoint.sh).

This fixes the fatal error:
  failed to get encryption key: failed to save key:
  open /tmp/pulse-test-data/.encryption.key: permission denied

Related to #695

tests/integration/docker-compose.test.yml

@@ -37,14 +37,14 @@ services:
       - TZ=UTC
       # Point to mock GitHub server
       - PULSE_UPDATE_SERVER=http://mock-github:8080
-      # Test database in memory
-      - PULSE_DATA_DIR=/tmp/pulse-test-data
+      # Use /data which is already owned by pulse user via entrypoint
+      - PULSE_DATA_DIR=/data
       # Enable debug logging
       - PULSE_LOG_LEVEL=debug
       # Mock mode for faster testing
       - PULSE_MOCK_MODE=true
     volumes:
-      - test-data:/tmp/pulse-test-data
+      - test-data:/data
     depends_on:
       mock-github:
         condition: service_healthy