docs: comprehensive analysis and decision for PR #43 vs PR #62

Created detailed strategic decision document comparing:
- PR #43: Full build system overhaul (esbuild, ESM/CJS/browser)
- PR #62: Simple runtime guards for process/document

Decision: Merge PR #62 (modified)

Rationale:
- PR #43 is outdated (v1.2.2 vs current v1.3.0)
- PR #43 has breaking changes and high risk
- PR #62 solves immediate user pain point (Cloudflare Workers)
- Defer ESM/browser bundles to v2.0 with modern tooling

This decision resolves issue #42 while preserving all v1.3.0
features and fixes. Future ESM support can use 2025 best practices
rather than 2022-era esbuild approach.

Author: claude