Documentation

PR Description

## Summary
- What this PR does (bullet points)

## Test Plan
- How to verify it works

## Related Issues
- Resolves #123

Changelog Entry

### [VERSION] - [DATE]

#### New Features
- **Feature Name**: Brief description

#### Improvements
- **Improvement**: What changed and why

#### Bug Fixes
- **Fix**: What was broken (#issue)

#### Breaking Changes
- **Change**: What breaks, migration steps

Feature Documentation

When documenting a feature, cover:

User Impact

• What capability does this add?
• How do users access it?

Technical Changes

• API changes (endpoints, params)
• SDK changes (new methods)
• Database migrations
• Config changes

Breaking Changes (if any)

• What breaks
• Migration steps

Key Files

• CHANGELOG.md - Self-hosted deployment changelog (breaking/critical changes only)
• apps/opik-documentation/documentation/fern/docs/changelog/ - Main product docs changelog entries (dated .mdx files)
• apps/opik-documentation/documentation/fern/docs/agent_optimization/getting_started/changelog.mdx - Agent Optimizer release changelog
• apps/opik-documentation/documentation/fern/docs.yml - Docs routing/navigation source of truth for changelog surfaces
• .github/release-drafter.yml - Release template

Changelog Routing Rules

• Pick the changelog target by scope; do not default everything to root CHANGELOG.md.
• Use CHANGELOG.md only for self-hosted deployment breaking/critical/security-impacting notes.
• Use apps/opik-documentation/documentation/fern/docs/changelog/*.mdx for general Opik product release notes shown in /docs/opik/changelog.
• Use apps/opik-documentation/documentation/fern/docs/agent_optimization/getting_started/changelog.mdx for Agent Optimizer version updates (for example sdks/opik_optimizer releases like 3.1.0).
• Liquibase changelog.xml files are migration manifests, not user-facing release-note changelogs.
• If unsure where an entry belongs, confirm the surface from apps/opik-documentation/documentation/fern/docs.yml before editing.

Images in documentation

• Use fern/img for documentation images (e.g. apps/opik-documentation/documentation/fern/img/...).
• Do not use static/img for new assets; it is a legacy folder used by external integrations and cannot be deleted.
• Reference images in docs as /img/... (e.g. /img/tracing/openai_integration.png).
• In repos that define docs.yaml/docs.yml, treat that file as the routing source of truth; do not assume URLs mirror directory layout.

Internationalized READMEs

Non-English README files (readme_CN.md, readme_ES.md, readme_FR.md, readme_DE.md) are AI machine-translated from the English README.md.

• Each non-English README must have a notice at the top (as a blockquote) warning that the file is AI-translated and welcoming improvements.
• When the English README is updated with significant content changes, re-translate the affected non-English READMEs using AI and update accordingly.
• Do not manually edit translated READMEs for content changes; update the English source and re-translate.

Style

• User perspective, not implementation details
• Specific (version numbers, dates)
• Code examples for API/SDK changes
• Concise - link to docs, don't duplicate