refactor(hubspot): deduplicate expert-consultation and newsletter form logic

[samuv]

This is a stacked PR that need to be merged after this

• Extract shared HubSpot submission logic, dismissal check, and constants into renderer/src/common/lib/hubspot.ts
• Add useHubSpotForm hook for consent state, instance ID fetching, and pre-wired submit function
• Extract shared dialog leaf components (HubSpotDialogContent, SuccessDialogContent, ConsentCheckbox, PrivacyFooter) into hubspot-form-parts.tsx
• Migrate both expert-consultation banner and newsletter modal to use shared utilities, hook, and components
• Pass instance_id as a hidden field in both HubSpot form submissions

[samuv]

/build-test

[github-actions]

Build Artifacts for PR #1771

Platform	Architecture	Status
macOS	arm64	✅ Ready
macOS	x64	✅ Ready
Windows	arm64	✅ Ready
Windows	x64	✅ Ready
Linux	arm64	✅ Ready
Linux	x64	✅ Ready

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Version: pr-1771 | Artifacts expire in 7 days | Triggered by @samuv

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