docs: Clarify why no multiple values or repeated keys

[roottool]

Description

Add a dedicated section explaining why safe-formdata treats repeated keys as boundary violations.

This clarifies that while multiple values may be semantically valid in application logic, their interpretation necessarily implies structural decisions (arrays, sets, ordering, merging rules) that are outside the scope of safe-formdata's strict, non-inferential boundary model.

Boundary Checklist (Required)

safe-formdata enforces a strict trust boundary for FormData.
If any item below does not apply, this change likely does not belong here.

• No interpretation

  • Key names are treated as opaque strings
  • No structural inference ([], ., brackets, paths, etc.)

• No silent behavior

  • No merging, overwriting, auto-fixing, or implicit resolution
  • All boundary violations are reported explicitly

• Boundary respected

  • No validation, coercion, schema, framework conventions, or business logic

📘 Boundary rules & non-goals:
https://github.com/roottool/safe-formdata/blob/main/AGENTS.md

Type of Change

• Bug fix
• Security fix
• Documentation
• Refactoring (no behavior change)
• Tests
• Tooling / CI

Testing

Documentation-only change. No code modifications.

---

🤖 Generated with Claude Code

Co-Authored-By: Claude [email protected]

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (42eb33a) to head (9ae1320).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main       #25   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            3         3           
  Lines           22        22           
  Branches         6         6           
=========================================
  Hits            22        22           

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.