Add Docker Containers to Q1 2026 roadmap (#271)

## Summary

Adds Docker Containers feature to the Q1 2026 roadmap and timeline
diagram. Also adds CUA node to the timeline diagram (it existed in
content but was missing from the visual).

## Changes

- **Mermaid diagram**: Added Q1D (CUA) and Q1E (Docker Containers) nodes
to timeline
- **Roadmap section**: Added Docker Containers section with three image
types and usage examples
- **Detailed plan**: Created comprehensive plan at
`docs/plans/docker-containers.mdx` with:
  - Three image specifications (Linux, Windows, Development)
  - Complete Dockerfiles and entrypoint scripts
  - Port mappings, environment variables, security considerations
  - Claude Code sandboxing configuration for dev image
- **Navigation**: Added plan to `docs.json`
- **Updated**: Roadmap date to January 27, 2026

## Images

1. **Linux Runtime** (`amd/gaia:linux`) - GAIA pre-installed via pip
2. **Windows Runtime** (`amd/gaia:windows`) - GAIA pre-installed via pip
3. **Development** (`amd/gaia:dev`) - Full dev environment with Claude
Code

All images are self-contained and accessed via `docker exec -it`.

Closes #270

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Co-authored-by: Claude Sonnet 4.5 <noreply@anthropic.com>
Co-authored-by: Kalin Ovtcharov <kalin@extropolis.ai>

Author: 3 people

.gitignore

@@ -108,6 +108,11 @@ ENV/
 # IDE settings
 .idea/
 
+# macOS
+.DS_Store
+.AppleDouble
+.LSOverride
+
 # Node.js
 node_modules/
 npm-debug.log*

docs/docs.json

@@ -310,6 +310,7 @@
               "plans/chat-ui",
               "plans/mcp-client",
               "plans/cua",
+              "plans/docker-containers",
               "plans/image-agent",
               "plans/mcp-docs"
             ]