Default pod root to an OS-specific user-data dir instead of ./data #5

Problem

config.json currently sets root: "./data", which main.js resolves relative to the install directory. That breaks pod persistence in the two most common launch modes:

• npx solid-desktop → resolves under ~/.npm/_npx/<hash>/node_modules/solid-desktop/data. The path is versioned and not guaranteed to survive npm cache cleanups or package upgrades.
• npm install -g solid-desktop → resolves under the global node_modules location, which is often non-writable without sudo (and is the wrong place for user data anyway).

Even in git clone + npm start use, the data lives inside the working tree — so git clean or moving the repo loses the pod.

Desktop apps normally store user data in OS-specific locations:

• Linux: ~/.config/<app>/… (Electron's default for userData) or ~/.local/share/<app>/… (XDG_DATA_HOME)
• macOS: ~/Library/Application Support/<app>/…
• Windows: %APPDATA%\<app>\…

Electron exposes this via app.getPath('userData'), which returns the right per-OS path automatically.

Proposal

Default the pod root to path.join(app.getPath('userData'), 'pod'). Keep the config.json override so power users can point at a specific dir (USB drive, NAS, shared volume). Drop the literal "root": "./data" from the committed config.json so the OS-specific default kicks in unless explicitly overridden.

Resolved paths would be:

• Linux: ~/.config/solid-desktop/pod
• macOS: ~/Library/Application Support/solid-desktop/pod
• Windows: %APPDATA%\solid-desktop\pod

Migration

Anyone already running 0.0.6 with content in the repo's ./data would need to move that folder once to the new location, or set config.json root to the old absolute path to keep using it in place. For a fresh install there's no migration — the new default just works.

Worth deciding whether to ship a one-time migration shim that detects an existing in-tree ./data and copies/moves it on first launch of the new version, or to handle it purely via release notes.

Out of scope

Multi-pod / pod-switcher UX. The single-default-root model stays; this issue is only about where that root lives by default.