feat: Add get_notifications tool to scrape LinkedIn notifications

[andrema2]

Summary

Add a new get_notifications tool that scrapes the LinkedIn notifications page (/notifications/) and returns structured notification items. Currently, the notifications page is only used internally by find_unreplied_comments to detect comment notifications, but there's no way to retrieve all notifications.

Motivation

Users want to check their LinkedIn notifications through the MCP server — new connection requests, post reactions, mentions, endorsements, job alerts, etc. The existing find_unreplied_comments already navigates to /notifications/ but only filters for comment-related items. A dedicated tool would expose all notification types.

Proposed Solution

• Add get_notifications() scraping function in scraping/posts.py that navigates to /notifications/, scrolls to load content, and extracts all notification items with their type, text, link, and timestamp
• Register a get_notifications MCP tool in tools/posts.py
• Return structured list: {notifications: [{text, link, type, created_at}]}
• Support a limit parameter (default 20)

Acceptance Criteria

• get_notifications scraping function implemented
• MCP tool registered and accessible
• Unit tests for scraping function
• Tool-level tests
• Documentation updated (README, AGENTS.md, docs/docker-hub.md)