feat(.github): Add GitHub workflows from hve-core

[WilliamBerryiii]

Summary

Migrate GitHub workflows from microsoft/hve-core to this repository, implementing a hybrid linting approach.

Workflows to Implement

Core Linting (HVE-Core Pattern)

• spell-check.yml - CSpell spell checking
• markdown-lint.yml - Markdown style linting
• table-format.yml - Markdown table formatting
• markdown-link-check.yml - Broken link detection

Unified Linting (MegaLinter)

• megalinter.yml - Python, Shell, Terraform, YAML linting

Security

• codeql-analysis.yml - Python security scanning
• dependency-review.yml - Vulnerable dependency review

Orchestrators

• pr-validation.yml - PR checks orchestrator
• main.yml - Main branch CI orchestrator

Prerequisites

• PR chore(settings): migrate cspell to modular dictionary structure #15 (cspell migration) merged
• package.json created for npm-based tooling