Root cause: CREATE TABLE graph_nodes in Go migration (graph_sqlite.go)
was missing 'pagerank REAL DEFAULT 1.0' per DESIGN.md spec.
Fix:
- Go: add pagerank to CREATE TABLE + migrateAddColumn() for existing DBs
- Rust: replace .ok() hack with ensure_column() that checks pragma_table_info
before ALTER TABLE, making it properly idempotent with explicit error handling
- Rust: warn+skip if column still missing (rather than silent continue)
xiaowei