fix(vector-store): fix PostgreSQL DeleteByPrefix and update namespace defaults

[AbirAbbas]

Summary

• Fix DeleteByPrefix to use PostgreSQL || operator for LIKE pattern - the previous approach with prefix+"%" in Go wasn't working correctly with parameter binding
• Change default namespace from "documentation" to "website-docs" to match the frontend chat API expectations
• Add scope: "global" to clear_namespace API call to ensure proper scope matching

Root Cause

The delete namespace API was returning deleted: 0 even when vectors existed because:

1. The PostgreSQL LIKE pattern wasn't being constructed correctly through parameter binding
2. The scope wasn't being explicitly passed, causing a mismatch

Test plan

• Deploy control plane with the fix
• Run curl -X DELETE .../api/v1/memory/vector/namespace -d '{"namespace":"website-docs", "scope":"global"}' and verify it deletes vectors
• Re-run reindex script and verify vectors are created
• Test chat functionality returns TypeScript examples

🤖 Generated with Claude Code