fix: Add null safety checks for audience.type and audience.segment_type

[bokelley]

Problem

The targeting browser was throwing a JavaScript error when rendering audiences that don't have a type property:

TypeError: undefined is not an object (evaluating 'audience.type.replace')

Console logs showed:

• 255 custom targeting keys loaded successfully
• Error occurred on line 533 of targeting browser when rendering audiences
• Some audiences from GAM don't include type, segment_type, or status fields

Solution

Added conditional rendering for audience properties that may be undefined:

Changes in templates/targeting_browser.html:

1. Line 532-534: Only render type badge if audience.type exists
2. Line 541: Only render segment_type badge if audience.segment_type exists
3. Line 542: Added null check for audience.status before comparing

Before:

<span class="badge">${audience.type.replace('_', ' ')}</span>
<span class="badge">${audience.segment_type}</span>
${audience.status !== 'ACTIVE' ? ... : ''}

After:

${audience.type ? `<span class="badge">${audience.type.replace('_', ' ')}</span>` : ''}
${audience.segment_type ? `<span class="badge">${audience.segment_type}</span>` : ''}
${audience.status && audience.status !== 'ACTIVE' ? ... : ''}

Impact

• ✅ Targeting browser now renders all audiences without JavaScript errors
• ✅ Audiences without type/segment_type/status simply don't show those badges
• ✅ No impact on functionality - purely defensive coding

Testing

• Verified error was on line 533 with audience.type.replace
• Added null checks for all audience properties that could be undefined
• Change is template-only, no backend logic affected

Related to PR #681 which fixed similar field name mismatch in product targeting selector.