fix: handle compound shell commands in output filter matchers

[bug-ops]

Summary

• Fix output filter matchers not triggering when LLMs generate compound shell commands like cd /path && cargo test 2>&1 | tail -80
• CommandMatcher::matches now extracts the last command segment from &&/; chains, stripping trailing pipes and redirections before matching
• Root cause of filter metrics not appearing in TUI despite fix: propagate filter_stats to TUI metrics in native tool path #480 fix: filters never matched because the first token was cd, not cargo

Changes

• zeph-tools/filter/mod.rs — split matches into matches_single + compound fallback via extract_last_command; 4 new tests

Test plan

• cargo nextest run -p zeph-tools --lib — 344 passed, 0 failed
• cargo clippy --workspace -- -D warnings — clean
• Manual: run with --tui, verify filter stats appear in Resources panel for LLM-generated compound commands