docs: improve PR template with enhanced structure and flexibility

[roottool]

Description

Improve the PR template to provide better guidance for contributors and align with AGENTS.md design rules. This change adds structured sections for security impact, API stability, and testing verification while maintaining flexibility for different PR types.

Type of Change

• Documentation (changes to documentation only)

Boundary Checklist (Required for Implementation Changes)

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

For documentation, tooling, or CI changes: You may skip this section by checking the box below and explaining why.

• This is a non-implementation change (Documentation, Tooling, or CI only)
  • Reason: PR template is documentation/process improvement, not parser implementation

Security & API Stability

Security Impact:

• No impact on security (no changes to forbidden keys, prototype safety)
• Reviewed against security rules in AGENTS.md

API Contract:

• No changes to public API (parse function signature, type definitions)
• No breaking changes to ParseResult, ParseIssue, or IssueCode

Versioning:

• Change is compatible with current v0.x versioning policy

Testing

Automated Checks:

• TypeScript type checking passes (bun run check:type:source)
• All tests pass (bun run test)
• Build succeeds (bun run build)

Additional Verification:

• Template markdown syntax verified (checkboxes, lists, links)
• Tested with different PR scenarios:
  • Implementation change: All boundary checklist items required
  • Documentation change: Skip option works correctly
  • Security fix: Security & API Stability section captures relevant info

Changes

Key improvements:

1. Flexible Boundary Checklist

   • Added skip option for non-implementation changes (Documentation, Tooling, CI)
   • Maintains strict requirements for implementation changes
   • Addresses issue from PR docs: improve documentation with JSDoc and reorganized README for v0.1.3 #44 where checklist needed manual interpretation

2. Security & API Stability section (new)

   • Security Impact: forbidden keys, prototype safety checks
   • API Contract: Breaking change detection
   • Versioning: v0.x policy compliance
   • Directly implements AGENTS.md Security rules (lines 76-95) and API contract (lines 138-199)

3. Structured Testing section

   • Automated Checks: Type checking, tests, build (with commands)
   • Additional Verification: Manual testing and edge cases
   • Aligns with actual PR practice (see PR docs: improve documentation with JSDoc and reorganized README for v0.1.3 #44 detailed verification)

4. Automated Review section (new)

   • Claude Code: boundary-validator skill guidance
   • Other tools: Links to AGENTS.md and skills directory
   • Promotes self-review and skill adoption

5. Type of Change improvements

   • Moved to top for better visibility
   • Added descriptions for each option
   • Clearer categorization

Benefits:

• Better PR quality through structured guidance
• Reduced ambiguity for non-implementation changes
• Explicit security and API stability checks
• Tool-agnostic design (removed tool-specific signatures)
• Aligned with AGENTS.md design principles

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (42b75ca) to head (12c5eab).
⚠️ Report is 9 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main       #49   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            3         3           
  Lines           22        22           
  Branches         6         6           
=========================================
  Hits            22        22           

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