Fix local development console errors

[areibman]

📥 Pull Request

📘 Description
This PR resolves numerous console errors encountered during local development, primarily caused by misconfigured or missing environment variables for PostHog analytics and backend API connections.

The changes include:

• Graceful PostHog Handling: PostHog analytics are now disabled by default in local development when NEXT_PUBLIC_POSTHOG_KEY is not provided, preventing 401/404 and MIME type errors. PostHog components now gracefully handle uninitialized PostHog instances.
• Local Setup Guide: A new LOCAL_DEVELOPMENT_SETUP.md guide has been added to streamline the local environment setup, covering Supabase configuration, backend API instructions, and common troubleshooting steps.

🧪 Testing
The changes were validated by:

• Running the application in local development mode with an empty NEXT_PUBLIC_POSTHOG_KEY to confirm the absence of PostHog-related console errors.
• Verifying that PostHog components (provider, page view, user identifier) function correctly or gracefully exit when PostHog is not initialized.
• Reviewing the LOCAL_DEVELOPMENT_SETUP.md for clarity and accuracy of instructions.

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