feat(parser): classify parser failures

[stacknil]

Summary

• add parser failure categories for unsupported lines: unknown_timestamp, unknown_program, known_program_unknown_message, malformed_source_ip, unsupported_pam_variant
• expose failure_categories and warning category fields in Markdown, JSON, and warnings.csv
• update parser/report tests, golden report fixtures, noisy parser matrix, and reviewer-facing docs

Validation

• cmake -S . -B build
• cmake --build build
• ctest --test-dir build -C Debug --output-on-failure
• git diff --check
• privacy/safety scan for local paths, private identifiers, and secret-like patterns