Polish beta docs and generator cleanup

[dfed]

Summary

• remove the empty README subsection and tighten the Xcode/Swift package integration headings
• update the direct SafeDITool migration example to match the current manifest-based generate command
• remove an unused local in ScopeGenerator to keep source builds warning-free

Test plan

• ./CLI/lint.sh
• swift test --traits sourceBuild

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (5b5032b) to head (ee0454c).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #253   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           41        41           
  Lines         6213      6212    -1     
=========================================
- Hits          6213      6212    -1     

Files with missing lines	Coverage Δ
Sources/SafeDICore/Generators/ScopeGenerator.swift	100.00% <ø> (ø)

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