Hide already registered clients in thv client setup

[carlos-gn]

Summary

• Filters out clients that are already registered in all selected groups from the client selection step in thv client setup
• When all installed clients are already registered for the selected groups, exits early with a clear message
• Handles both interactive group selection (multiple groups) and auto-selected groups (single group)

Closes #1308

Test plan

• Unit tests for FilterClientsAlreadyRegistered covering all edge cases
• Unit tests for setupModel.Update verifying group-to-client transition filtering
• Unit tests for client selection toggle and confirmation behavior
• Manual testing: verify clients already registered in all selected groups are hidden
• Manual testing: verify clients registered in only some groups still appear
• Manual testing: verify "all clients registered" message when no clients remain

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 67.20%. Comparing base (65f28eb) to head (4ece54a).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3889      +/-   ##
==========================================
+ Coverage   67.18%   67.20%   +0.02%     
==========================================
  Files         448      449       +1     
  Lines       45218    45236      +18     
==========================================
+ Hits        30380    30402      +22     
+ Misses      12469    12462       -7     
- Partials     2369     2372       +3     

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