fix(conflict): stage resolved files before checking for remaining conflicts

[jafreck]

Problem

The conflict-resolver agent successfully removes conflict markers from files, but git still reports them as "Unmerged" because the agent doesn't git add the resolved files. The post-agent check uses git diff --name-only --diff-filter=U, which only clears when files are staged — so it always reports all files as unresolved even when the content is clean.

Confirmed on TAAD issues #20 (7 files) and #25 (6 files): all files had 0 conflict markers but were still listed as "both modified" / unmerged.

Fix

Stage the conflicted files with git add after the agent runs and before checking for remaining conflicts. Files with real remaining conflict markers will fail to stage (git rejects staging files with markers), so the check still catches genuinely unresolved files.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 92.96%. Comparing base (9241611) to head (ee26e7b).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/core/fleet-orchestrator.ts	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #355      +/-   ##
==========================================
- Coverage   92.97%   92.96%   -0.01%     
==========================================
  Files         194      194              
  Lines       19855    19856       +1     
  Branches     3118     3118              
==========================================
  Hits        18460    18460              
- Misses       1361     1362       +1     
  Partials       34       34              

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