docs: update all docs for polish session — copy/paste, theme hot-swap, tests, drag-resize
- progress.md: add session log for copy/paste, theme hot-swap, tree enhancements,
session resume, drag-resize, testing, CI, Deno PoC
- phases.md: mark completed items (copy/paste, drag-resize, tree click, subtree cost,
session resume, CI signing)
- task_plan.md: update theme decision (hot-swap works), add new decisions
- CLAUDE.md: add test paths, test commands, vitest dep
- .claude/CLAUDE.md: fix stale deferred items and theme limitation
- README.md: update feature summary
- TODO.md: move 7 completed items, update active list
- CHANGELOG.md: add session entries under [Unreleased]
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