feat(paths): use XDG base directories instead of ~/.plannotator

[cwrau]

Summary

• Adds packages/shared/paths.ts with three helpers: getDataBase(), getStateBase(), getConfigBase()
• Stores persistent data (plans/, history/) under $XDG_DATA_HOME/plannotator (default: ~/.local/share/plannotator)
• Stores ephemeral state (drafts/, sessions/, debug logs) under $XDG_STATE_HOME/plannotator (default: ~/.local/state/plannotator)
• Stores configuration (config.json, improvement hooks) under $XDG_CONFIG_HOME/plannotator (default: ~/.config/plannotator)
• Existing installations are unaffected: if ~/.plannotator already exists on disk, all three helpers return it — zero migration required

Call sites updated

File	Change
packages/shared/storage.ts	getDataBase() for plans + history
packages/shared/draft.ts	getStateBase() for drafts
packages/shared/config.ts	getConfigBase() for config.json
packages/shared/improvement-hooks.ts	getConfigBase() for hooks dir
packages/server/sessions.ts	getStateBase() for sessions
packages/server/codex-review.ts	getStateBase() for schema file + debug log

Migration for existing users

No action needed — ~/.plannotator continues to work unchanged. To adopt XDG paths, simply move the directory:

mv ~/.plannotator ~/.local/share/plannotator   # data + state
# or symlink: ln -s ~/.local/share/plannotator ~/.plannotator

Config and state can be split further if desired:

mkdir -p ~/.config/plannotator ~/.local/state/plannotator
mv ~/.local/share/plannotator/config.json ~/.config/plannotator/
mv ~/.local/share/plannotator/hooks      ~/.config/plannotator/
mv ~/.local/share/plannotator/drafts     ~/.local/state/plannotator/
mv ~/.local/share/plannotator/sessions   ~/.local/state/plannotator/

Test plan

• Fresh install: verify data lands in ~/.local/share/plannotator/, state in ~/.local/state/plannotator/, config in ~/.config/plannotator/
• With ~/.plannotator present: verify all paths still resolve to ~/.plannotator (no regression)
• Custom XDG_DATA_HOME, XDG_STATE_HOME, XDG_CONFIG_HOME: verify respected on fresh install

🤖 Generated with Claude Code

[backnotprop]

I understand this on one hand. And the code organization is great.

On the other, this is a fairly big lift I need to just map out mentally.

Also, there is a lot of convenience in ~/ dot directories.