add migration guide for breaking changes across versions #106

Summary

Pre-1.0 versions may include breaking changes in minor bumps. Users upgrading need a clear migration guide showing what changed, what breaks, and how to fix it.

Prior Work

Website#77 (closed 2026-06-09) established the CHANGELOG page and a migration template with the 0.4→0.5 guide. The page exists at /changelog/. This issue extends that foundation to cover additional versions and the 0.5.0 release.

Remaining Scope

0.5.0 Migration Section

ergo was bumped to 0.5.0 (PR#152, merged 2026-06-11). Key changes that need migration guidance:

• validate shorthand form (ergo#135) — new feature, no breaking change, but document the new option
• responseSchema option (ergo#137) — new feature for send()/handler(), document opt-in usage
• onResponse lifecycle hook (ergo#140) — new feature for handler()/createRouter(), document usage
• catchHandler 4th argument (ergo-router#105) — backwards-compatible (existing 3-arg handlers unaffected), document new capability
• New presets: sse, webhooks, public (ergo-router#106) — new feature, document availability
• body:false + validate.body detection (ergo-router#104) — potentially breaking: misconfigurations that previously caused runtime 500 errors now throw at registration time
• Multi-runtime CI (ergo#138) — informational: Deno and Bun compatibility verified
• Naming audit decision (ergo#139) — informational: send, accepts, compose names retained

Version Coverage Gaps

• Review whether all pre-0.4 breaking changes are documented
• Add migration sections for any gaps in the 0.1→0.2→0.3 range

Acceptance Criteria

• 0.5.0 migration section added to existing CHANGELOG page
• Each breaking/notable change has before/after code examples
• Potentially breaking changes (body:false + validate.body) are called out prominently
• Earlier version gaps are filled or marked as not applicable
• Cross-linked from package pages and Getting Started

Related

• Add CHANGELOG page and migration guide for 0.4→0.5 #77 — established CHANGELOG page and 0.4→0.5 template (closed)
• 1.0 stability milestone: define criteria and timeline ergo#128 — 1.0 stability milestone ("Migration guide exists for each pre-1.0 version")
• chore: bump version to 0.5.0 and finalize CHANGELOG ergo#152 — 0.5.0 version bump PR