chore(services): Add IsNil method for ServiceState

[tab]

• Implemented IsNil() to check for nil service or FSM
• Updated service nil checks to use IsNil() in controllers and models
• Added unit tests for IsNil() method

[Copilot]

Pull request overview

This PR introduces a new IsNil() method to the ServiceState struct to encapsulate nil checks for both the service instance and its FSM field. The implementation replaces multiple repetitive nil check patterns throughout the codebase with a single, centralized method call.

Changes:

• Added IsNil() method to ServiceState that checks if the service or its FSM is nil
• Refactored controller methods (Start, Stop, Restart) to use IsNil() instead of inline nil checks
• Updated UI handler methods (handleStopKey, handleRestartKey) to use IsNil()

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
internal/app/ui/services/model.go	Implements the new IsNil() method on ServiceState
internal/app/ui/services/model_test.go	Adds comprehensive unit tests for the IsNil() method covering nil service, nil FSM, and valid service scenarios
internal/app/ui/services/controller.go	Replaces inline nil checks with IsNil() calls in Start, Stop, and Restart methods
internal/app/ui/services/update.go	Replaces inline nil checks with IsNil() calls in handleStopKey and handleRestartKey methods

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[codecov-commenter]

Codecov Report

❌ Patch coverage is 71.42857% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 87.46%. Comparing base (8a0b32a) to head (f202a66).

Files with missing lines	Patch %	Lines
internal/app/ui/services/update.go	0.00%	2 Missing ⚠️

❌ Your patch status has failed because the patch coverage (71.42%) is below the target coverage (80.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@           Coverage Diff           @@
##           master      #47   +/-   ##
=======================================
  Coverage   87.45%   87.46%           
=======================================
  Files          34       34           
  Lines        2582     2584    +2     
=======================================
+ Hits         2258     2260    +2     
  Misses        285      285           
  Partials       39       39           

Files with missing lines	Coverage Δ
internal/app/ui/services/controller.go	96.87% <100.00%> (ø)
internal/app/ui/services/model.go	57.01% <100.00%> (+0.76%)	⬆️
internal/app/ui/services/update.go	50.45% <0.00%> (ø)

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