feat(notebooks): add filtered content search

[andyjmorgan]

Summary

• replace the unfiltered v1 notebook list implementation with v2 notebook search
• support optional text queries, structured API filters, sorting, and a default limit of 20
• preserve backend totals and report returned and truncated result metadata
• keep pup notebooks list as a hidden compatibility alias
• make notebook validation errors readable

Testing

• cargo fmt --check
• git diff --check
• cargo test commands::notebooks::tests -- --test-threads=1 — 9 passed
• cargo clippy --all-targets -- -D warnings