feat: Add content calendar with GitHub Projects

Description

Create a GitHub Projects board for content planning, scheduling, and tracking.

Problem

• No centralized content planning
• Difficult to track what content is in progress
• No visibility into content pipeline
• Hard to plan content around themes/events
• No editorial calendar

Benefits

• Visual content pipeline
• Better planning and coordination
• Track content from idea to publication
• Identify gaps in content coverage
• Plan seasonal/event-based content
• Coordinate with contributors

Proposed Board Structure

Columns

1. Ideas - Raw content ideas
2. Backlog - Approved ideas
3. In Progress - Currently being written
4. In Review - Ready for review
5. Ready to Publish - Scheduled content
6. Published - Live content

Labels

• content:post - Blog post
• content:guide - Multi-part guide
• content:quiz - Quiz
• content:game - Interactive game
• content:exercise - Coding exercise
• priority:high - Urgent content
• priority:medium - Normal priority
• priority:low - Nice to have

Custom Fields

• Publish Date - Target publication date
• Author - Content creator
• Category - DevOps, Cloud, Security, etc.
• Status - Draft, Review, Scheduled, Published

Acceptance Criteria

• Create GitHub Project board
• Set up columns/workflow
• Create custom labels
• Add custom fields
• Document content workflow
• Add existing open issues to board
• Create issue templates for content ideas
• Document how to use board in CONTRIBUTING.md
• Set up automation (move cards on PR merge)

Resources

• GitHub Projects Documentation
• Editorial calendar best practices

Files to Modify

• .github/ISSUE_TEMPLATE/content-idea.yml - New template
• CONTRIBUTING.md - Add content workflow section
• docs/content-calendar.md - New documentation