Preserve manual titles across /clear

/clear creates a deferred successor session. Remember the current title only when its persisted provenance is manual, then rename the successor before it attaches and before its first prompt.

The existing session catalog is the durable source of title provenance after a reload. Live rename events provide the same provenance without another read. /new, /reset, session navigation, and workspace changes discard the carry.

Automatic and legacy titles with unknown provenance are never carried.