ROADMAP #4.44.5: Ship/provenance events — implement §4.44.5

Adds structured ship provenance surface to eliminate delivery-path opacity:

New lane events:
- ship.prepared — intent to ship established
- ship.commits_selected — commit range locked
- ship.merged — merge completed with provenance
- ship.pushed_main — delivery to main confirmed

ShipProvenance struct carries:
- source_branch, base_commit
- commit_count, commit_range
- merge_method (direct_push/fast_forward/merge_commit/squash_merge/rebase_merge)
- actor, pr_number

Constructor methods added to LaneEvent for all four ship events.

Tests:
- Wire value serialization for ship events
- Round-trip deserialization
- Canonical event name coverage

Runtime: 465 tests pass
ROADMAP updated with IMPLEMENTED status

This closes the gap where 56 commits pushed to main had no structured
provenance trail — now emits first-class events for clawhip consumption.

rust/crates/runtime/src/lib.rs

@@ -86,7 +86,8 @@ pub use lane_events::{
     compute_event_fingerprint, dedupe_superseded_commit_events, dedupe_terminal_events,
     is_terminal_event, BlockedSubphase, EventProvenance, LaneCommitProvenance, LaneEvent,
     LaneEventBlocker, LaneEventBuilder, LaneEventMetadata, LaneEventName, LaneEventStatus,
-    LaneFailureClass, LaneOwnership, SessionIdentity, WatcherAction,
+    LaneFailureClass, LaneOwnership, SessionIdentity, ShipMergeMethod, ShipProvenance,
+    WatcherAction,
 };
 pub use mcp::{
     mcp_server_signature, mcp_tool_name, mcp_tool_prefix, normalize_name_for_mcp,