style(base-chain): fix heading hierarchy for improved structure and SEO

[Earnwithalee7890]

What changed? Why?

This PR corrects heading hierarchy issues across Base Chain documentation to ensure proper semantic structure. The changes fix heading levels (h1, h2, h3, etc.) to follow a logical, sequential order without skipping levels, which improves both accessibility and SEO.

Files updated:

• Base Chain documentation pages with heading hierarchy issues
• All headings now follow proper sequential order (h1 → h2 → h3, etc.)
• No heading levels are skipped in the document structure

Proper heading hierarchy provides:

• Better SEO - Search engines use heading structure to understand content organization
• Improved accessibility - Screen readers rely on heading hierarchy for navigation
• Enhanced readability - Logical structure helps all users scan and understand content
• Consistent documentation - Standardized structure across all pages

Notes to reviewers

• Heading content remains unchanged; only heading levels have been adjusted
• Each page maintains a single h1 (typically the page title in frontmatter)
• Subsequent headings follow logical nesting without skipping levels
• Changes follow documentation best practices and WCAG 2.1 guidelines
• No functional changes to the documentation

How has it been tested?

• Manually verified heading hierarchy on each updated page
• Confirmed no heading levels are skipped (e.g., h2 → h4)
• Validated that page outlines are logical and properly nested
• Checked that documentation builds successfully
• Reviewed table of contents generation to ensure proper structure
• Tested screen reader navigation on updated pages

[cb-heimdall]

🟡 Heimdall Review Status

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