Refactor command handling and tag reconciliation

[ncode]

Summary

Refactors TagIt command execution and tag updates into smaller, testable units.

• Moves shared Cobra/Viper input resolution and command dependencies into dedicated command helpers.
• Extracts managed tag reconciliation, scheduler behavior, and Consul service registration updates.
• Updates systemd generation to render an explicit ExecStart invocation from shared command input.
• Documents the TAGIT_* environment variable precedence and shared validation path.
• Adds focused coverage for the refactored command, scheduler, registration, and TagIt helper paths.

Impact

The CLI paths now share validation and construction logic, while tag cleanup and reconciliation preserve unmanaged Consul tags through a focused reconciler. The systemd command now uses the same input resolution path as run and cleanup, with separate tests for invocation rendering.

Validation

• go test ./cmd ./pkg/tagit ./pkg/consul
• go test -coverpkg=./... ./... -race -coverprofile=coverage.out -covermode=atomic

[codecov]

Codecov Report

❌ Patch coverage is 98.45679% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 96.09%. Comparing base (1fa5cf2) to head (87d9c06).

Files with missing lines	Patch %	Lines
cmd/systemd.go	83.33%	2 Missing and 2 partials ⚠️
cmd/intake.go	98.61%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #47      +/-   ##
==========================================
+ Coverage   89.94%   96.09%   +6.14%     
==========================================
  Files           8       13       +5     
  Lines         368      512     +144     
==========================================
+ Hits          331      492     +161     
+ Misses         25       14      -11     
+ Partials       12        6       -6     

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