docs: Improve docs navigation & support resources

[pixelflips]

Description

Improves Storybook documentation navigation and support resources to help users find help and contribute more easily.

Fixes: DSS-7

Changes

• Created "Get Support" page with direct Slack channel links, Linear board, and GitHub resources
• Reorganized the Contributing page with a task-based flow for better clarity
• Standardized all documentation links to use pds-link component for consistent styling
• Removed blank "Design Principles" page

Type of change

• This change requires a documentation update

Checklist:

If not applicable, leave options unchecked.

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing tests pass locally with my changes
• Design has QA'ed and approved this PR

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