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/memory/src/consolidate/input.rs

@@ -243,7 +243,7 @@ mod tests {
         let (_id, _) = write_staging(
             &layout,
             SourceRef {
-                session_id: "s".into(),
+                segment_id: "s".into(),
                 range: [0, 1],
             },
             ExtractedPayload::default(),

crates/memory/src/consolidate/lock.rs

@@ -260,7 +260,7 @@ mod tests {
         let (id_a, _) = write_staging(
             &layout,
             SourceRef {
-                session_id: "s".into(),
+                segment_id: "s".into(),
                 range: [0, 0],
             },
             ExtractedPayload::default(),
@@ -269,7 +269,7 @@ mod tests {
         let (id_b, _) = write_staging(
             &layout,
             SourceRef {
-                session_id: "s".into(),
+                segment_id: "s".into(),
                 range: [1, 1],
             },
             ExtractedPayload::default(),

crates/memory/src/consolidate/staging.rs

@@ -94,9 +94,9 @@ mod tests {
         ExtractedPayload::default()
     }
 
-    fn source(session_id: &str, range: [u64; 2]) -> SourceRef {
+    fn source(segment_id: &str, range: [u64; 2]) -> SourceRef {
         SourceRef {
-            session_id: session_id.into(),
+            segment_id: segment_id.into(),
             range,
         }
     }

crates/memory/src/consolidate/tidy.rs

@@ -305,7 +305,7 @@ mod tests {
     fn flags_sources_overflow() {
         let (dir, layout) = workspace();
         let many_sources: String = (0..15)
-            .map(|i| format!("  - session_id: s{i}\n    range: [{i}, {i}]\n"))
+            .map(|i| format!("  - segment_id: s{i}\n    range: [{i}, {i}]\n"))
             .collect();
         write(
             &dir.path().join(".insomnia/memory/decisions/big.md"),