test: expand test coverage from 7 to 65 cases

[proxyBug]

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Summary

• Grows the test suite from 7 to 65 test cases across 14 test classes
• Adds first-ever coverage for cli.py, render_json, render_table, format_report, and all collection-orchestration functions
• All tests use mocks so they run offline with no real ss, netstat, docker, or /proc access

What's new

Area	Classes added	Key scenarios
_safe_int	SafeIntTests	valid int, non-numeric, empty, None
parse_process_field	ParseProcessFieldTests	single process, systemd preference, all-systemd fallback
parse_netstat_line	ParseNetstatLineTests	TCP LISTEN, UDP (UNCONN state), header skip, too-few-fields
lookup_user	LookupUserTests	None pid, missing /proc, PermissionError, uid→name resolution
infer_systemd_unit	InferSystemdUnitTests	None pid, missing cgroup file, service unit extraction
_dedupe_notes	DedupNotesTests	dedup, blank filtering, order preservation
collect_listening_sockets	CollectListeningSocketsTests	ss success, netstat fallback, no tools, ss stderr note
collect_docker_containers	CollectDockerContainersTests	not installed, ps failure, successful JSON parse
collect_inventory	CollectInventoryTests	docker skip, note merging, note dedup
render_json	RenderJsonTests	valid JSON, newline, endpoint fields
render_table	RenderTableTests	section headers, column headers, data, empty message, notes
format_report	FormatReportTests	json/table/markdown dispatch, unknown-format fallback
build_parser	BuildParserTests	defaults, --no-docker, --no-systemd, --format, --output
main	MainTests	no subcommand→1, scan→0, flag forwarding, file output

Test plan

• python -m unittest discover -s tests -v → 65 passed, 0 failed

https://claude.ai/code/session_01LFeBf9uLHNE2vu4fodoNnh
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