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/session-metrics/src/lib.rs

@@ -18,7 +18,7 @@
 use std::collections::BTreeMap;
 
 use serde::{Deserialize, Serialize};
-use session_store::{SessionId, Store, StoreError, save_extension, session_log};
+use session_store::{SegmentId, Store, StoreError, save_extension, segment_log};
 
 /// Domain tag used in `LogEntry::Extension` for all metrics records.
 pub const DOMAIN: &str = "metrics";
@@ -48,7 +48,7 @@ impl Metric {
     pub fn now(name: impl Into<String>) -> Self {
         Self {
             name: name.into(),
-            ts: session_log::now_millis(),
+            ts: segment_log::now_millis(),
             dimensions: BTreeMap::new(),
             value: None,
             correlation_id: None,
@@ -77,11 +77,11 @@ impl Metric {
 /// （メトリクスのために本体処理を止めるかは呼び出し側の判断）。
 pub fn record_metric(
     store: &impl Store,
-    session_id: SessionId,
+    segment_id: SegmentId,
     metric: &Metric,
 ) -> Result<(), StoreError> {
     let payload = serde_json::to_value(metric).expect("Metric serialization cannot fail");
-    save_extension(store, session_id, DOMAIN, payload)
+    save_extension(store, segment_id, DOMAIN, payload)
 }
 
 /// `RestoredState.extensions` から metrics domain の payload を順に取り出し、