Clean up client filtering after PR #3889

[JAORMX]

Summary

PR #3889 added client filtering in thv client setup. Code review identified four mechanical cleanup items — no behavior changes, just improved consistency and safety.

• Move ErrAllClientsRegistered sentinel from cmd/thv/app/ui/ to pkg/client/ to match project convention (sentinel errors live in pkg/)
• Replace hand-rolled inner loop with slices.Contains in isClientRegisteredInAllGroups, matching the pattern used in pkg/groups/skills.go
• Extract selectedGroups() helper to deduplicate the map-to-groups-slice logic shared by filterClientsBySelectedGroups() and RunClientSetup()
• Add bounds check on group indices before indexing m.Groups to guard against out-of-bounds panics

Type of change

• Refactoring (no behavior change)

Test plan

• Unit tests (task test)
• Linting (task lint-fix)

Changes

File	Change
pkg/client/filter.go	Add ErrAllClientsRegistered sentinel, use slices.Contains
cmd/thv/app/ui/clients_setup.go	Remove local sentinel, extract selectedGroups() with bounds check, use it in filterClientsBySelectedGroups, sortedSelectedGroupNames, and RunClientSetup
cmd/thv/app/client.go	Update ui.ErrAllClientsRegistered → client.ErrAllClientsRegistered
cmd/thv/app/ui/selected_groups_test.go	New tests for bounds check and out-of-bounds filtering

Does this introduce a user-facing change?

No

Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 68.62%. Comparing base (0ad68d6) to head (514a072).
⚠️ Report is 14 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4095      +/-   ##
==========================================
+ Coverage   68.56%   68.62%   +0.05%     
==========================================
  Files         448      448              
  Lines       45779    45774       -5     
==========================================
+ Hits        31389    31411      +22     
+ Misses      11967    11943      -24     
+ Partials     2423     2420       -3     

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