Move SymbolCandidatesTest to tests/Integration

[Firehed]

All three cases in SymbolCandidatesTest drive the real SymbolSource over fixtures (even the one that already stubs CodeResolverInterface still uses the real source for its sanity assertion). It is integration-shaped — move it to tests/Integration/ rather than try to make it a true unit test.

Pure git mv + namespace change.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.73%. Comparing base (1565cb7) to head (e67b14b).
⚠️ Report is 1 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff            @@
##               main     #670   +/-   ##
=========================================
  Coverage     99.73%   99.73%           
  Complexity     1903     1903           
=========================================
  Files           136      136           
  Lines          4882     4882           
=========================================
  Hits           4869     4869           
  Misses           13       13           

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