Echoes arc "The Outward Turn" complete — new era begins at Ch1073

The Echoes story arc concluded at Ch1072 "The Outward Turn" with story-bible.md updated for canon continuity. The new arc — beginning at Ch1073 — introduces thought-probes and song-ships as narrative devices, with the Weavers discovering an Anomaly that allows them to paint a universe. The arc runs through Ch1104 "The End of the Beginning," suggesting a meta-narrative about creation itself.