refactor(app): Deduplicate string literals into constants

[tab]

• Convert CommandType from an int enum to string constants
• Reference the command-name constants in the cobra flag and Use definitions
• Extract the API action names into actionStart, actionStop and actionRestart constants
• Reuse config.AppName for the root command
• Reuse IndicatorDot for the blink full frame

[sentry]

Codecov Report

❌ Patch coverage is 94.44444% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 89.82%. Comparing base (5b23344) to head (e796630).

Files with missing lines	Patch %	Lines
internal/app/doctor/environment.go	0.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #146      +/-   ##
==========================================
+ Coverage   89.71%   89.82%   +0.10%     
==========================================
  Files          76       76              
  Lines        7448     7430      -18     
==========================================
- Hits         6682     6674       -8     
+ Misses        601      592       -9     
+ Partials      165      164       -1     

Files with missing lines	Coverage Δ
internal/app/api/handler.go	100.00% <100.00%> (ø)
internal/app/cli/commands.go	100.00% <100.00%> (+6.17%)	⬆️
internal/app/tracer/tracer.go	100.00% <100.00%> (ø)
internal/app/ui/components/blink.go	96.87% <ø> (ø)
internal/app/ui/services/view.go	96.91% <ø> (-0.02%)	⬇️
internal/config/sentry/identity.go	100.00% <ø> (ø)
internal/app/doctor/environment.go	81.48% <0.00%> (ø)

... and 3 files with indirect coverage changes

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