Refactor/gatsby node modularization

[Manishnemade12]

Description

refactor/gatsby-node-modularization-issue-5 --title "[gatsby-node] Modularize createPages handlers for blog, Kanvas labs, and Sistent" --body "Description

Closes : #7615
This PR modularizes targeted parts of gatsby-node.js to reduce merge conflicts and improve maintainability.

What changed

• Added src/node-api/createBlogPages.js for blog post, category, and tag page creation.
• Added src/node-api/createKanvasLabPages.js for Kanvas lab page creation.
• Added src/node-api/createSistentComponentPages.js for Sistent component page creation.
• Updated gatsby-node.js to orchestrate these handlers through dependency injection (graphql, createPage, reporter, templates/helpers).
• Removed the extracted GraphQL fragments and page-creation loops from the monolithic createPages export.

Scope control

• Only issue-relevant areas were refactored (blog/category/tags, kanvas-labs, sistent).
• No unrelated routing behavior, templates, or node lifecycle APIs were modified.

Validation

• Attempted targeted lint on changed files:
  • npx eslint gatsby-node.js src/node-api/createBlogPages.js src/node-api/createKanvasLabPages.js src/node-api/createSistentComponentPages.js
• Lint execution is currently blocked in this environment due to missing local dependency: Cannot find module 'globals' from eslint.config.js.

Notes for Reviewers

• Functional behavior for extracted pages is preserved (same path patterns and page context).
• gatsby-node.js now acts as a cleaner orchestrator for these concerns.

Signed commits

• Yes, I signed my commits.

[Manishnemade12]

@rishiraj38 can you please review this pr