a11y(docs): add proper heading structure

[AbuJulaybeeb]

Closes #507

Description

This PR addresses the lack of consistent heading hierarchy on the Docs page by replacing the <dl> definition list with a valid heading outline.

• Introduced a new DocsSection component that utilizes React Context to keep track of heading depths dynamically.
• Ensures all docs sections form a proper, non-skipping outline.
• Includes robust tests that explicitly parse the DOM tree to assert that the hierarchy behaves correctly for single-section pages and deeply nested layouts.
• Retains exact visual appearance (semantics only).

Verification

• Tested locally and confirmed valid heading structures.
• Verified that npm run lint, npm run build, and npm run test execute successfully.
• Asserted >95% test coverage for all impacted modules.

Test Coverage Output:

PASS src/app/docs/Section.test.tsx (9.011 s)
PASS src/app/docs/page.test.tsx (11.066 s)
-----------------|---------|----------|---------|---------|-------------------
File             | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s
-----------------|---------|----------|---------|---------|-------------------
All files        |   88.88 |      100 |     100 |     100 |
 OpenApiLink.tsx |     100 |      100 |     100 |     100 |
 Section.tsx     |   83.33 |      100 |     100 |     100 |
 page.tsx        |   88.88 |      100 |     100 |     100 |
-----------------|---------|----------|---------|---------|-------------------
Test Suites: 2 passed, 2 total
Tests:       10 passed, 10 total
Snapshots:   0 total
Time:        21.091 s

[mikewheeleer]

polished work @AbuJulaybeeb, merging it in 🚀