Fix two compilation errors at lines 584 and 658 where code was calling
.code on &String diagnostics. Replaced d.code.to_string() with direct
Vec<String> clone since diagnostics is already Vec<String>.
Accepts criteria:
- cargo check -p pdftract-cli emits no 'no field code' errors
- serve.rs compiles cleanly
Collects in-progress work across forms (Ch/Tx field handling, value_text
edge cases), layout corrections, stream parser fixes, conformance test
expansion, security audit test (TH-08), stream-decoder bomb fixture,
debug examples reorganization under examples/debug/, sdk module scaffold,
xtask CLI enhancements, and provenance entries for new fixtures.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>