fix: add semantic headings to right sidebar

[mittalsonal]

Summary

• Replaced the RightSidebar top label with an h2 and each sidebar panel title with h3 semantic headings.
• Added a test that verifies the heading hierarchy for screen reader navigation.
• Cleaned up same-file lint findings surfaced by the touched component so the PR remains CI-ready.

Closes #2082

Changes Made

• Preserved existing visual classes/styles while changing panel title markup from generic div/span elements to heading tags.
• Updated RightSidebar.test.tsx mocks to match the current component contract.
• Added semantic heading assertions for Constraints, Time Controls, Planner Constraints, Manual Satellite, and LEO Decay Monitor.

Testing

• npm test -- --run src/__tests__/RightSidebar.test.tsx - passed (3 tests)
• npm run typecheck - passed
• npx eslint src/components/RightSidebar.tsx src/__tests__/RightSidebar.test.tsx --format json - clean
• npm run build - passed
• git diff --cached --check - passed

Edge Cases

• Visual styling is preserved by keeping existing class names and inline styles.
• Heading hierarchy starts at the sidebar title (h2) and panel titles use h3 consistently.
• No unrelated workspace changes are included.

Screenshots

Not applicable - semantic markup/test-only accessibility improvement with no intended visual change.

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[mittalsonal]

Maintainer note: GitHub typecheck is passing and the PR is mergeable. The label workflow failed because the auto-label action attempted to add a label from the fork context (Resource not accessible by integration); I updated the PR body to avoid triggering that auto-label path, but I do not have permission to rerun the failed upstream workflow. The Vercel check is also blocked by repository deployment authorization, not by this change.