feat: persist TOC open/closed state per file in localStorage

[k1LoW]

Summary

• Save and restore TOC panel open/closed state per file in localStorage (key: mo-toc-open)
• Non-markdown files always have ToC closed regardless of stored state
• Remove the auto-close useEffect in favor of derived state

Closes #138

[github-actions]

Code Metrics Report

	main (aaeae71)	#143 (b7b3d66)	+/-
Coverage	57.2%	57.2%	0.0%
Code to Test Ratio	1:0.5	1:0.5	+0.0
Test Execution Time	29s	30s	+1s

Details

  |                     | main (aaeae71) | #143 (b7b3d66) | +/-  |
  |---------------------|----------------|----------------|------|
  | Coverage            |          57.2% |          57.2% | 0.0% |
  |   Files             |             39 |             39 |    0 |
  |   Lines             |           3272 |           3272 |    0 |
  |   Covered           |           1873 |           1873 |    0 |
+ | Code to Test Ratio  |          1:0.5 |          1:0.5 | +0.0 |
  |   Code              |           5085 |           5117 |  +32 |
+ |   Test              |           2846 |           2888 |  +42 |
- | Test Execution Time |            29s |            30s |  +1s |

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Reported by octocov

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.