Generate submission-ready paper package

[Zefan-Cai]

Summary

This PR isolates TODO 7 from the larger CLI branch: generate a submission-oriented paper package for Stage 07 on top of zefan-todo-4.

What Changed

• added src/platform/foundry.py
• added generate_paper_package(...)
• generates a paper package with:
  • abstract.md
  • manuscript.tex
  • references.bib
  • tables.tex
  • figure_manifest.json
  • build.sh
  • submission_checklist.md
  • compiled PDF placeholder artifact
• wired Stage 07 approval to generate the paper package
• added focused regression coverage in tests/test_foundry_paper_package.py

Base

• base branch: zefan-todo-4

Scope

This PR is intentionally limited to TODO 7 only.

Not included here:

• review/dissemination package generation
• CI wiring

Validation

• python -m py_compile main.py src/*.py tests/*.py
• python -m unittest tests.test_foundry_paper_package tests.test_writing_pipeline -v