Update Core Vitest Configuration

[nathanvale]

Task: Update Core Vitest Configuration

Description

Replace complex zombie management configuration with simplified 5-line Vitest
config using modern pool: 'forks' approach for stable process isolation.

Acceptance Criteria

• Update vitest.config.ts with simplified configuration
• Implement pool: 'forks' for stable process isolation
• Set teardownTimeout: 20_000 for cleanup time
• Enable isolate: true for clean worker lifecycle
• Configure fileParallelism: true for controlled concurrency
• Add CI stability configuration (bail on first failure)

Technical Details

• Implementation approach: Replace existing vitest.config.ts with simplified
  version
• Key considerations:
  • Preserve existing test setup files that aren't zombie-related
  • Ensure CI compatibility with bail configuration
  • Maintain performance while improving stability
• Code locations/files affected:
  • vitest.config.ts (primary file)
  • Possibly environment-specific configurations

Dependencies

• Task 003 completed (backup commit created)
• Vitest 3.2+ already available (confirmed in epic)
• No conflicting vitest configurations

Effort Estimate

• Size: S
• Hours: 1
• Parallel: false (conflicts with other config changes)

Definition of Done

• vitest.config.ts updated with 5-line zombie prevention config
• Pool configuration set to 'forks'
• Teardown timeout set to 20 seconds
• Isolation and file parallelism properly configured
• CI bail configuration added
• Configuration syntax validated
• No breaking changes to existing test setup