Fix #109: Add LCS to MaximumIndependentSet reduction

[zazabap]

Summary

• Adds implementation plan for LongestCommonSubsequence model and LCS → MaximumIndependentSet reduction rule
• Plan covers: LCS model implementation, match-graph reduction (Apostolico & Guerra, 1987), unit tests, example program, paper documentation, and export regeneration

Closes #109

[codecov]

Codecov Report

❌ Patch coverage is 98.11321% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 96.89%. Comparing base (a88812b) to head (7eac728).
⚠️ Report is 141 commits behind head on main.

Files with missing lines	Patch %	Lines
.../longestcommonsubsequence_maximumindependentset.rs	95.89%	3 Missing ⚠️
.../longestcommonsubsequence_maximumindependentset.rs	96.25%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #173      +/-   ##
==========================================
+ Coverage   96.88%   96.89%   +0.01%     
==========================================
  Files         200      204       +4     
  Lines       27537    27855     +318     
==========================================
+ Hits        26680    26991     +311     
- Misses        857      864       +7     

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[isPANN]

On Hold: Branch is severely out of date with main (11 merge conflicts in core files including src/lib.rs, src/rules/mod.rs, docs/paper/reductions.typ). The reduction logic itself is correct and well-tested, but resolving conflicts would be more work than reimplementing from scratch on current main.

Plan: Close this PR and reimplement issue #109 fresh on current main using issue-to-pr. The LCS model already exists on main (PR #598), so only the rule + tests + paper entry need to be added.

Additionally, the DOI corrections and overhead expression fixes flagged in the issue quality check should be addressed in the reimplementation.