docs: fix broken Commerce Web API links (#460)

[dshevtsov]

Purpose of this pull request

Fixes #460 by updating broken Adobe Developer documentation links across the Commerce PHP documentation.

The changes replace obsolete index.html URLs with the current trailing-slash routes for:

• GraphQL documentation
• Inventory REST documentation

A total of 67 published pages were updated. Markdown linting passes with no issues.

Affected pages

This is a representative sample; the complete change affects 67 pages.

• https://developer.adobe.com/commerce/php/architecture/technical-vision/web-api
• https://developer.adobe.com/commerce/php/module-reference/module-inventory
• https://developer.adobe.com/commerce/php/module-reference/module-inventory-admin-ui
• https://developer.adobe.com/commerce/php/module-reference/module-inventory-graph-ql
• https://developer.adobe.com/commerce/php/module-reference/module-inventory-multi-dimensional-indexer-api

Follow-up action item

• Deliver the corresponding module-reference/ link updates to the original module source-code repositories so future generated documentation remains correct.

[github-actions]

🔍 Linter Report

Click to expand full report

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                     LINTER REPORT
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Generated: 2026-09-22T19:48:22.031Z
Mode: Full Linting (all rules + dead links check)
Target Directory: /home/runner/work/commerce-php/commerce-php
Skipped Rules:
  - check-frontmatter → src/pages/includes

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Files to process: 67


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                        SUMMARY
═══════════════════════════════════════════════════════════════

  📁 Files processed:    67
  📄 Files with issues:  0
  ❌ Total errors:       0
  ⚠️  Total warnings:     0
  📋 Total issues:       0

Result: ✅ PASSED - All files passed linting successfully!

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