feat(policy): add lane reconciliation events and policy support

Add terminal lane states for when a lane discovers its work is already
landed in main, superseded by another lane, or has an empty diff:

LaneEventName:
- lane.reconciled — branch already merged, no action needed
- lane.merged — work successfully merged
- lane.superseded — work replaced by another lane/commit
- lane.closed — lane manually closed

PolicyAction::Reconcile with ReconcileReason enum:
- AlreadyMerged — branch tip already in main
- Superseded — another lane landed the same work
- EmptyDiff — PR would be empty
- ManualClose — operator closed the lane

PolicyCondition::LaneReconciled — matches lanes that reached a
no-action-required terminal state.

LaneContext::reconciled() constructor for lanes that discovered
they have nothing to do.

This closes the gap where lanes like 9404-9410 could discover
'nothing to do' but had no typed terminal state to express it.
The policy engine can now auto-closeout reconciled lanes instead
of leaving them in limbo.

Addresses ROADMAP P1.3 (lane-completion emitter) groundwork.

Tests: 4 new tests covering reconcile rule firing, context defaults,
non-reconciled lanes not triggering reconcile rules, and reason
variant distinctness. Full workspace suite: 643 pass, 0 fail.

rust/crates/tools/src/lib.rs

@@ -2144,6 +2144,14 @@ enum LaneEventName {
     Finished,
     #[serde(rename = "lane.failed")]
     Failed,
+    #[serde(rename = "lane.reconciled")]
+    Reconciled,
+    #[serde(rename = "lane.merged")]
+    Merged,
+    #[serde(rename = "lane.superseded")]
+    Superseded,
+    #[serde(rename = "lane.closed")]
+    Closed,
 }
 
 #[derive(Debug, Clone, Serialize, Deserialize, PartialEq, Eq)]