update: SessionId / SessionStart / SessionOrigin 等を Segment 系名称へ

- Type/Function/Variantを Segment* 系へ統一
  - SessionId/SessionStart/SessionOrigin/SessionStartState/SessionState/SessionLogSink/SessionLockInfo
  - new_session_id / session_id / create_session* / list_sessions / lookup_session / update_session / find_by_session
  - protocol Event::SessionRotated → SegmentRotated、CompactDone.new_session_id → new_segment_id
- Module: session_log → segment_log / session → segment (file mv 含む)
  pod 側の session_log_sink → segment_log_sink も同様
- crate 名 (session-store)、CLI flag (--session)、ResumeWithSession (CLI tied) は据え置き
- session-tests/session_metrics_test 等の Store impl も追従

crates/tui/src/ui.rs

@@ -1019,10 +1019,10 @@ fn render_compact(lines: &mut Vec<Line<'static>>, evt: &CompactEvent, width: u16
             )
         }
         CompactEvent::Done {
-            new_session_id,
+            new_segment_id,
             elapsed_secs,
         } => {
-            let short = new_session_id
+            let short = new_segment_id
                 .to_string()
                 .chars()
                 .take(8)