feat: support multiple compliance documents (PDFs, URLs, markdown) for PR review

[Copilot]

The tool previously accepted only a single --doc source. Organizations maintain compliance requirements across multiple documents (architecture standards, security policies, company guidelines) and PRs need to be checked against all of them simultaneously.

Changes

• cli.py — --doc now uses Click multiple=True; repeat the flag for each source
• doc_loader.py — added load_documents(sources: List[str]) -> List[ArchitectureDoc]; wraps existing load_document per source
• reviewer.py — _build_prompt, _parse_response, and run_review now accept List[ArchitectureDoc]; prompt includes a clearly labelled section per document
• types.py — ReviewResult gains compliance_docs: List[ArchitectureDoc] for full audit trail
• reporter.py — meta.compliance_docs written to the JSON report (source + doc_type per entry)
• README.md — updated CLI examples, report schema table, example JSON, and GitHub Actions workflow

Usage

# backwards-compatible single doc
python -m src.cli review --owner myorg --repo myrepo --pr 42 \
  --doc docs/architecture.pdf

# multiple sources — any mix of PDF, URL, text/markdown
python -m src.cli review --owner myorg --repo myrepo --pr 42 \
  --doc docs/architecture.pdf \
  --doc https://intranet.corp/security-policy \
  --doc docs/company-guidelines.md

The AI prompt enumerates each document as a numbered, labelled section so the model can attribute violations to specific policies. The report meta block records which documents were consulted on each run.

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