fix: convert global command variables to local instances

[ivanauth]

Fixes #556

Summary

Tests running with -count=10 would panic with "flag redefined" errors. Package-level cobra.Command global variables were reused across test runs, causing flag registration conflicts when InitialiseRootCmd was called multiple times in the same process.

Changes

• Converted all register*Cmd functions to create fresh command instances locally instead of relying on global variables
• Modified 13 files (9 in internal/cmd, 4 in internal/commands)
• Added regression test TestMultipleInitialiseRootCmd to verify the fix

Test Plan

• All tests pass with go test -race -count=10 ./internal/cmd
• All tests pass with go test -race -count=10 ./internal/commands
• New regression test verifies InitialiseRootCmd can be called multiple times
• Commands still function correctly (zed version --help, zed schema --help)

This ensures InitialiseRootCmd is now idempotent and can be called multiple times without panicking.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 51.57895% with 138 lines in your changes missing coverage. Please review.
✅ Project coverage is 41.31%. Comparing base (7ed5ab0) to head (ddcdd6f).
⚠️ Report is 10 commits behind head on main.

Files with missing lines	Patch %	Lines
internal/commands/permission.go	0.00%	55 Missing ⚠️
internal/commands/relationship.go	0.00%	46 Missing ⚠️
internal/commands/watch.go	0.00%	15 Missing ⚠️
internal/cmd/schema.go	81.25%	7 Missing and 2 partials ⚠️
internal/commands/schema.go	0.00%	8 Missing ⚠️
internal/cmd/validate.go	76.19%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #566      +/-   ##
==========================================
+ Coverage   39.28%   41.31%   +2.02%     
==========================================
  Files          37       37              
  Lines        5448     5800     +352     
==========================================
+ Hits         2140     2396     +256     
- Misses       3063     3148      +85     
- Partials      245      256      +11     

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[tstirrat15]

I dig it. Thank you!