Major updates: LinkedIn auto-posting, timezone fixes, and Docker improvements

Features:
- Add LinkedIn OAuth integration and auto-posting functionality
- Add scheduler service for automated post publishing
- Add metadata field to generated_posts for LinkedIn URLs
- Add privacy policy page for LinkedIn API compliance
- Add company management features and employee accounts
- Add license key system for company registrations

Fixes:
- Fix timezone issues (use UTC consistently across app)
- Fix datetime serialization errors in database operations
- Fix scheduling timezone conversion (local time to UTC)
- Fix import errors (get_database -> db)

Infrastructure:
- Update Docker setup to use port 8001 (avoid conflicts)
- Add SSL support with nginx-proxy and Let's Encrypt
- Add LinkedIn setup documentation
- Add migration scripts for schema updates

Services:
- Add linkedin_service.py for LinkedIn API integration
- Add scheduler_service.py for background job processing
- Add storage_service.py for Supabase Storage
- Add email_service.py improvements
- Add encryption utilities for token storage

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

config/migrate_remove_linkedin_unique.sql

@@ -0,0 +1,7 @@
+-- Migration: Remove UNIQUE constraint from customers.linkedin_url
+-- This allows multiple customers (different ghostwriters/companies) to share the same LinkedIn URL.
+-- Each user context gets its own independent Customer record.
+
+ALTER TABLE customers DROP CONSTRAINT IF EXISTS customers_linkedin_url_key;
+
+-- The existing index idx_customers_linkedin_url remains for fast lookups (non-unique).