chore: add project meta files and Claude behavioral guide

Add TODO.md, CHANGELOG.md, .claude/CLAUDE.md behavioral guide.
Update README.md with v2 planning notice and docs links.
Fix .gitignore to scope CLAUDE.md exclusion to root only.

CHANGELOG.md

@@ -0,0 +1,17 @@
+# Changelog
+
+All notable changes to this project will be documented in this file.
+
+The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
+and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
+
+## [Unreleased]
+
+### Added
+- v2 architecture planning: Tauri 2.x + Svelte 5 + Claude Agent SDK via Node.js sidecar
+- Research documentation covering Agent SDK, xterm.js performance, Tauri ecosystem, and ultrawide layout patterns
+- Phased implementation plan (6 phases, MVP = Phases 1-4)
+- Error handling and testing strategy for v2
+- Documentation structure in `docs/` (task_plan, phases, findings, progress)
+- TODO.md for tracking active work
+- `.claude/CLAUDE.md` behavioral guide for Claude sessions