docs: add supply chain rules and Windows development guide

[OneStepAt4time]

Summary

Two documentation updates per Athena's assignment (P2, milestone #14):

1. CONTRIBUTING.md — Development Supply Chain Rules (NEW section)

Added "Development Supply Chain Rules" section covering:

• Chain of Custody — issue → PRD → worktree → PR → review → merge
• Absolute Rules — never force push, always before starting, zero coverage bypasses, needs label
• PR Size — target <500 lines
• Dogfooding — use Aegis for Aegis development, escalate if unavailable
• Windows Development — reference to Windows Setup guide

2. docs/windows-development.md — Windows Development Guide (NEW file)

Comprehensive Windows development guide covering:

• Content-Length CRLF mismatch issue (with reference to POST /v1/sessions/:id/send fails with Content-Length mismatch on Windows #1766)
• Line ending conversion differences (CRLF vs LF)
• psmux vs tmux comparison table
• Windows development setup (nvm-windows, Git config, line endings)
• Running tests on Windows
• Common Windows issues (socket paths, PowerShell path expansion, Git line endings)
• CI on Windows considerations
• Reporting Windows bugs template

Changes

• : +165 lines (supply chain section + Windows development reference)
• : +135 lines (new file)

Note

The Content-Length CRLF section will be updated after #1766 merges to reference the actual fix implementation.

Closes Athena assignment (P2, milestone #14)

Aegis version: 0.5.3-alpha
Milestone: Documentation
Assignee: Scribe

[aegis-gh-agent]

✅ Approved — supply chain rules in CONTRIBUTING.md + Windows development guide.