Test Coverage, CLAUDE.md, and README Footer

[cjimti]

Test Coverage Improvements

Before

• Total: 90.2%
• Core library (txeh.go): 96.8%
• CLI cmd package: 44.7%

After

• Total: 92.4%
• Core library (txeh.go): 96.8%
• CLI cmd package: 81.6%

What was added (txeh/cmd/root_test.go)

DryRun path tests for commands that were only tested in save mode:

• TestRemoveIPs_DryRun
• TestRemoveIPRanges_DryRun
• TestRemoveByComment_DryRun

VersionFromBuild tests:

• TestVersionFromBuild_GoreleaserVersion - covers the goreleaser-set version path
• TestVersionFromBuild_Default - covers the debug.ReadBuildInfo() path

initEtcHosts tests:

• TestInitEtcHosts_DefaultPath - covers NewHostsDefault() path (empty paths + zero max)
• TestInitEtcHosts_EmptyPathsNonZeroMax - covers NewHosts path with custom max

Cobra Args validation tests for all commands:

• TestAddCmd_Args_Valid, _TooFew, _InvalidIP, _InvalidHostname
• TestRemoveHostCmd_Args_Valid, _Empty, _InvalidHostname
• TestRemoveIPCmd_Args_Valid, _Empty, _InvalidIP
• TestRemoveCidrCmd_Args_Valid, _Empty, _InvalidCIDR
• TestRemoveCommentCmd_Args_Valid, _Empty
• TestListByHostsCmd_Args_Valid, _Empty, _InvalidHostname
• TestListByIPCmd_Args_Valid, _Empty, _InvalidIP
• TestListByCidrCmd_Args_Valid, _Empty, _InvalidCIDR
• TestListByCommentCmd_Args_Valid, _Empty
• TestShowCmd_Args

Cobra Run function tests for all commands:

• TestAddCmd_Run_Basic, _WithComment, _NotQuiet, _NotQuiet_WithComment
• TestRemoveHostCmd_Run, TestRemoveIPCmd_Run, TestRemoveCidrCmd_Run, TestRemoveCommentCmd_Run
• TestListByHostsCmd_Run, TestListByIPCmd_Run, TestListByCidrCmd_Run, TestListByCommentCmd_Run
• TestShowCmd_Run, TestVersionCmd_Run

Remaining uncovered code

• os.Exit(1) error paths in cmd functions (require process forking to test)
• Execute() function (cobra wrapper, 0%)
• main() in txeh/txeh.go (0%, standard for Go CLIs)

CLAUDE.md Updates

• Fixed verify-full description (was incorrectly described as "Run all tests including integration")
• Added inline descriptions to Quick Reference make targets
• Added missing make targets: lint-fix, test-integration, test-e2e, dead-code, check, mutate
• Updated goreleaser command from v1 syntax to v2 (goreleaser release --snapshot --clean)
• Added GNUmakefile, test/integration/, test/e2e/ to File Naming Conventions table

README.md Footer

Added attribution footer before the link reference definition.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.90%. Comparing base (bedfe2c) to head (cfa2c72).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff             @@
##           master      #39       +/-   ##
===========================================
+ Coverage   72.48%   88.90%   +16.42%     
===========================================
  Files          15       15               
  Lines         676      676               
===========================================
+ Hits          490      601      +111     
+ Misses        165       60      -105     
+ Partials       21       15        -6     

see 12 files with indirect coverage changes

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