feat(tools): add lane_completion module (P1.3)

Implement automatic lane completion detection:
- detect_lane_completion(): checks session-finished + tests-green + pushed
- evaluate_completed_lane(): triggers CloseoutLane + CleanupSession actions
- 6 tests covering all conditions

Bridges the gap where LaneContext::completed was a passive bool
that nothing automatically set. Now completion is auto-detected.

ROADMAP P1.3 marked done.

rust/crates/tools/src/lib.rs

@@ -4793,6 +4793,8 @@ fn parse_skill_description(contents: &str) -> Option<String> {
     None
 }
 
+pub mod lane_completion;
+
 #[cfg(test)]
 mod tests {
     use std::collections::BTreeMap;