Keep latest session selection tied to real session recency

The next repo-local sweep target was ROADMAP #72: the `latest`
managed-session alias could depend on filesystem mtime before the
session's own persisted recency markers, which made the selection
path vulnerable to coarse or misleading file timestamps. The fix
promotes `updated_at_ms` into the summary/order path, keeps CLI
wrappers in sync, and locks the mtime-vs-session-recency case with
regression coverage.

Constraint: Preserve existing managed-session storage layout while changing only the ordering signal
Rejected: Keep sorting by filesystem mtime and just sleep longer in tests | hides the semantic ordering bug instead of fixing it
Confidence: high
Scope-risk: narrow
Reversibility: clean
Directive: Any future managed-session ordering change must keep runtime and CLI summary structs aligned on the same recency fields
Tested: cargo fmt --all --check; cargo clippy --workspace --all-targets -- -D warnings; cargo test --workspace; architect review APPROVE
Not-tested: Cross-filesystem behavior where persisted session JSON cannot be read and fallback ordering uses mtime only

rust/crates/rusty-claude-cli/src/main.rs

@@ -3122,6 +3122,7 @@ struct SessionHandle {
 struct ManagedSessionSummary {
     id: String,
     path: PathBuf,
+    updated_at_ms: u64,
     modified_epoch_millis: u128,
     message_count: usize,
     parent_session_id: Option<String>,
@@ -4711,6 +4712,7 @@ fn list_managed_sessions() -> Result<Vec<ManagedSessionSummary>, Box<dyn std::er
         .map(|session| ManagedSessionSummary {
             id: session.id,
             path: session.path,
+            updated_at_ms: session.updated_at_ms,
             modified_epoch_millis: session.modified_epoch_millis,
             message_count: session.message_count,
             parent_session_id: session.parent_session_id,
@@ -4726,6 +4728,7 @@ fn latest_managed_session() -> Result<ManagedSessionSummary, Box<dyn std::error:
     Ok(ManagedSessionSummary {
         id: session.id,
         path: session.path,
+        updated_at_ms: session.updated_at_ms,
         modified_epoch_millis: session.modified_epoch_millis,
         message_count: session.message_count,
         parent_session_id: session.parent_session_id,