Update CHANGELOG.md and docs for session tree release
CHANGELOG.md:
- Add /tree command, context event, before_agent_start event
- Add ui.custom(), branch summarization, selectedBg theme color
- Add snake game example hook
- Add external contributions: CRLF fix, bash on Unix, clickable OAuth, error messages
- Update theme requirements (50 total colors)
session.md:
- Complete rewrite for v2 tree structure
- Document all entry types with examples
- Add SessionManager API reference
hooks.md:
- Replace pi.send() with pi.sendMessage()
- Add pi.appendEntry(), pi.registerCommand(), pi.registerMessageRenderer()
- Move exec() from ctx to pi.exec()
- Add ui.custom() for custom TUI components
- Add context and before_agent_start events
- Update before_compact event fields
- Add ctx.sessionManager and ctx.modelRegistry
Mario Zechner
a9479458ee