docs: README for condenser module

[csmith49]

Summary

This PR adds a simple README file for the condenser module to help explain design decisions and the expected condensation flow.

Checklist

• If the PR is changing/adding functionality, are there tests to reflect this?
• If there is an example, have you run the example to make sure that it works?
• If there are instructions on how to run the code, have you followed the instructions and made sure that it works?
• If the feature is significant enough to require documentation, is there a PR open on the OpenHands/docs repository with the same branch name?
• Is the github CI passing?

---

Agent Server images for this PR

• GHCR package: https://github.com/OpenHands/agent-sdk/pkgs/container/agent-server

Variants & Base Images

Variant	Architectures	Base Image	Docs / Tags
java	amd64, arm64	eclipse-temurin:17-jdk	Link
python	amd64, arm64	nikolaik/python-nodejs:python3.12-nodejs22	Link
golang	amd64, arm64	golang:1.21-bookworm	Link

Pull (multi-arch manifest)

# Each variant is a multi-arch manifest supporting both amd64 and arm64
docker pull ghcr.io/openhands/agent-server:7470104-python

Run

docker run -it --rm \
  -p 8000:8000 \
  --name agent-server-7470104-python \
  ghcr.io/openhands/agent-server:7470104-python

All tags pushed for this build

ghcr.io/openhands/agent-server:7470104-golang-amd64
ghcr.io/openhands/agent-server:7470104-golang_tag_1.21-bookworm-amd64
ghcr.io/openhands/agent-server:7470104-golang-arm64
ghcr.io/openhands/agent-server:7470104-golang_tag_1.21-bookworm-arm64
ghcr.io/openhands/agent-server:7470104-java-amd64
ghcr.io/openhands/agent-server:7470104-eclipse-temurin_tag_17-jdk-amd64
ghcr.io/openhands/agent-server:7470104-java-arm64
ghcr.io/openhands/agent-server:7470104-eclipse-temurin_tag_17-jdk-arm64
ghcr.io/openhands/agent-server:7470104-python-amd64
ghcr.io/openhands/agent-server:7470104-nikolaik_s_python-nodejs_tag_python3.12-nodejs22-amd64
ghcr.io/openhands/agent-server:7470104-python-arm64
ghcr.io/openhands/agent-server:7470104-nikolaik_s_python-nodejs_tag_python3.12-nodejs22-arm64
ghcr.io/openhands/agent-server:7470104-golang
ghcr.io/openhands/agent-server:7470104-java
ghcr.io/openhands/agent-server:7470104-python

About Multi-Architecture Support

• Each variant tag (e.g., 7470104-python) is a multi-arch manifest supporting both amd64 and arm64
• Docker automatically pulls the correct architecture for your platform
• Individual architecture tags (e.g., 7470104-python-amd64) are also available if needed

[github-actions]

API breakage checks (Griffe)

Result: Failed

Log excerpt (first 1000 characters)

============================================================
Checking openhands-sdk (openhands.sdk)
============================================================
Comparing openhands-sdk 1.11.5 against 1.11.4
::notice title=openhands-sdk API::Ignoring Field metadata-only change (non-breaking): load_public_skills
::notice title=openhands-sdk API::Ignoring Field metadata-only change (non-breaking): temperature
::warning file=openhands-sdk/openhands/sdk/llm/llm.py,line=190,title=LLM.top_p::Attribute value was changed: `Field(default=1.0, ge=0, le=1)` -> `Field(default=None, ge=0, le=1, description='Nucleus sampling parameter. Defaults to None (uses provider default). Set to a value between 0 and 1 to control diversity of outputs.')`
::error title=SemVer::Breaking changes detected (1); require at least minor version bump from 1.11.x, but new is 1.11.5

============================================================
Checking openhands-workspace (openhands.workspace)
============================

Action log

[github-actions]

Agent server REST API breakage checks (OpenAPI)

Result: Passed

Action log

[all-hands-bot]

🟢 Good taste - Clear documentation that explains complex design decisions.

This README helps maintainers understand the condensation system architecture, event-based design, and failure handling strategies. All referenced file paths are valid, and the content accurately describes the design philosophy.

Verdict: ✅ Worth merging - Improves codebase understanding without any behavior changes.

Key Insight: Documentation that explains the "why" behind append-only event logs and condensation strategies is exactly what complex systems need.