feat: update --version output to include Go version and os/arch

[Copilot]

Summary

Updates the --version flag output to match the standardized format:

mcp-acronym-lookup version vX.Y.Z (goX.Y, os/arch)

Changes

• Added buildVersionOutput helper that normalizes the version string (adding a v prefix to bare semver strings) and appends the Go runtime version and OS/architecture via runtime.Version(), runtime.GOOS, and runtime.GOARCH
• Added --version flag to main() that prints the formatted version string and exits
• Added main_test.go with three tests covering: bare semver input, existing v-prefixed input, and non-semver (dev) input

Follows the same pattern applied to the hallucinateapi project in UnitVectorY-Labs/hallucinateapi#40.

[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 5.95%. Comparing base (194255d) to head (a8cf410).

Files with missing lines	Patch %	Lines
main.go	50.00%	5 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##            main     #89      +/-   ##
========================================
+ Coverage   0.00%   5.95%   +5.95%     
========================================
  Files          1       1              
  Lines         74      84      +10     
========================================
+ Hits           0       5       +5     
- Misses        74      79       +5     

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