fix: CLI QA improvements — docs, display, auto-JSON

[GiggleLiu]

Summary

• Fix docs/src/cli.md: replace all --edges with --graph to match actual CLI flag (14 occurrences)
• Fix docs typo suggestion example to use a close misspelling that actually triggers the hint
• Show full variant slash notation (Name/Graph/Weight) instead of diff-from-default
• Remove dead variant_to_slash function and unused HashSet import
• Deduplicate format_variant into shared variant_to_full_slash helper
• Auto-output JSON when stdout is piped for data commands (reduce, solve, evaluate, inspect)
• Add SpinGlass f64 weight inference from float syntax in --couplings/--fields
• Remove duplicate [default: 1] in help text (clap already shows it)
• Count reachable nodes (not unique problem names) in neighbor output

Test plan

• All 106 CLI tests pass (cargo test -p problemreductions-cli)
• No compiler warnings
• Manual QA: pred create MIS --graph 0-1,1-2 | pred solve - works
• Manual QA: pred show MaximumIndependentSe shows "Did you mean" suggestion
• Manual QA: pred to MIS --hops 2 shows full variant paths

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.88%. Comparing base (4ad5a83) to head (c3e6c2d).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #139   +/-   ##
=======================================
  Coverage   96.88%   96.88%           
=======================================
  Files         200      200           
  Lines       27537    27537           
=======================================
  Hits        26680    26680           
  Misses        857      857           

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