feat: implement email click tracking and custom redirect handler (#259)

[CodeSparks45]

This PR introduces a robust click-tracking mechanism for outbound campaign emails. It parses outgoing email bodies, rewrites anchor tags with a secure tracking URL, and handles the redirection while updating lead analytics.

Closes #259

Key Changes:

tasks.py: Implemented rewrite_email_links using BeautifulSoup to parse HTML. Used Django's cryptographic Signer to securely encode the campaign_lead_id and step_id within the tracking URL to prevent tampering. Intercepted the email body just before send_gmail.

views.py: Added ClickTrackingView (unauthenticated API endpoint). This decodes the secure token, updates the last_clicked_at timestamp on the specific CampaignLead, and gracefully handles the HttpResponseRedirect to the original URL.

urls.py: Registered the new /api/v1/clicks/track/ route for the interceptor.

Testing Performed:

Verified the link rewriting logic locally to ensure secure tokens generate correctly.

Tested the tracking endpoint to ensure it safely decodes the payload, updates database metrics, and redirects to the target destination without error.

[Kuldeeep18]

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