fix: configure non-interactive mode for CI apt-get installs

Ubuntu 24.04 CI was hanging on tzdata interactive timezone prompt.

Changes:
- tests/test_installer.sh: Set DEBIAN_FRONTEND=noninteractive, pre-configure timezone
- tests/test_installer.sh: Add apt-get options to suppress prompts
- .github/workflows/test.yml: Set environment variables in installer-test container
- install.sh: Auto-detect CI environment and enable non-interactive mode

This follows Debian/Ubuntu best practices for containerized environments and
prevents interactive prompts from blocking CI runs.

Fixes Ubuntu 24.04 installer-test CI failure.

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

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

.github/workflows/test.yml

@@ -131,6 +131,10 @@ jobs:
 
     container:
       image: ${{ matrix.os-image }}
+      env:
+        DEBIAN_FRONTEND: noninteractive
+        DEBCONF_NONINTERACTIVE_SEEN: "true"
+        TZ: UTC
 
     steps:
     - name: Checkout code