Address PR review comments: Pydantic v2 migration, configurable delays, demo data

[Copilot]

Fixes three issues identified in PR review: non-functional comparison UI due to empty state, deprecated Pydantic v1 API usage with v2 installed, and hardcoded timing constants.

Changes

• Frontend comparison page: Replace empty useState with hardcoded demo property IDs to enable query execution

  // Before: query never executes
  const [propertyIds] = useState<string[]>([])
  
  // After: query executes with demo data
  const propertyIds = ['property1', 'property2', 'property3']

• Pydantic v2 migration: Update @validator → @field_validator with correct v2 API

  # Before: deprecated v1 API
  @validator('shading_analysis', pre=True, always=True)
  def build_shading_analysis(cls, v, values):
  
  # After: v2 API with ValidationInfo
  @field_validator('shading_analysis', mode='before')
  @classmethod
  def build_shading_analysis(cls, v, info: ValidationInfo):
      values = info.data

• Google Ads sync delay: Extract hardcoded 5s sleep to GOOGLE_ADS_SYNC_DELAY_SECONDS config setting for environment-based configuration

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