- Fix ci/schema-gate.sh: Remove --lib --bins flags from cargo test command
The incorrect flags caused the test output parsing to fail, reporting
false negatives. Changed to 'cargo test --test json_schema'.
- Add notes/pdftract-2rc4.md: Verification note documenting all acceptance
criteria status. All criteria PASS: schema generation, migration tooling,
CI gate, and validation tests all functional.
Closes pdftract-2rc4
