Improve test coverage for buildinfo and webui packages

[aaronbrethorst]

Summary

Two packages have insufficient test coverage:

• internal/buildinfo/ — 0% coverage, no test file exists
• internal/webui/ — 53.5% coverage, has some tests but significant gaps

Acceptance criteria

• Create internal/buildinfo/buildinfo_test.go with tests for the package
• Identify untested code paths in internal/webui/ and add tests to bring coverage above 80%
• Follow existing test patterns in the repo (table-driven tests, testify assertions)
• make test passes
• make lint passes

Context

• internal/buildinfo/ is a small package that stores build metadata variables — a great starting point for writing a first Go test file
• internal/webui/ has 5 source files and 4 existing test files; examine the existing tests in index_handler_test.go, debug_index_handler_test.go, static_handler_test.go, and webui_coverage_test.go for patterns to follow
• Use make coverage to generate an HTML coverage report and identify specific uncovered lines

[Jason10293]

Working on this!