Clean up unique browser partitions on delete + drive-aware data defaults

[Kosinkadink]

Closes #1017

Summary

Two related disk/storage fixes for the launcher.

1. Browser partitions no longer leak on delete

Deleting an install previously only removed the install dir and the installations.json record. Unique-partition installs (browserPartition: 'unique') each own a persist:<id> bucket under userData/Partitions/<id> (cookies, IndexedDB, localStorage, service-worker cache, GPUCache). The id is unique per-install and never reused, so every create-unique -> delete cycle stranded one of these folders forever. (Copies were already safe: each copy gets a fresh id and its own deep-copied partition.)

handleDelete now, on both delete paths:

1. removes the install record first (so the user-visible delete is deterministic), then
2. best-effort cleans the partition - clears the session (clearStorageData, raced against a 5s timeout so it can never hang the operation or hold its lock) and removes Partitions/<id> (force + transient-lock retries).

Shared-partition installs are a no-op (they all share persist:shared, which must never be deleted). Worst case degrades to the old behavior (one folder left behind) - never a lock-up.

2. Large data dirs default to a sensible, grouped location

Previously the multi-GB consumers defaulted to the system drive even when the app was installed elsewhere, and on the common system-drive install they landed in poor spots: the install root and shared models/input/output under the home root, and the download cache under roaming AppData (which bloats roaming/AD profiles on login sync). These are still only defaults - users can override each in Settings.

Non-system-drive installs (e.g. app installed to D:) now group everything under a single <drive>\Comfy-Desktop parent instead of scattering at the drive root:

• <drive>\Comfy-Desktop\ComfyUI-Installs
• <drive>\Comfy-Desktop\ComfyUI-Shared (models / input / output)
• <drive>\Comfy-Desktop\ComfyUI-Cache\download-cache

System-drive Windows installs now distinguish new vs existing users:

• New installs group under %LOCALAPPDATA%\Comfy-Desktop (the standard per-user, non-roaming spot for large app data — and writable without admin, unlike a drive root):
  • %LOCALAPPDATA%\Comfy-Desktop\ComfyUI-Installs
  • %LOCALAPPDATA%\Comfy-Desktop\ComfyUI-Shared (models / input / output)
  • %LOCALAPPDATA%\Comfy-Desktop\ComfyUI-Cache\download-cache
• Existing installs keep their original home-root + roaming-cache layout — no data is moved or migrated.

New vs existing is classified from a home-root footprint (~/ComfyUI-Installs / ~/ComfyUI-Shared) and then pinned with a one-time marker (userData/data-location.json) so a user's chosen location can never flip on a later launch (e.g. if the legacy folders appear externally). The marker is written once at startup, never at module import. settings.json existence is deliberately not used as the signal (a new user creates it on first run).

Non-Windows behavior and the small Electron-managed userData state are unchanged (the latter intentionally stays on the system drive).

Changes

• src/main/lib/ipc/shared.ts - add deleteBrowserPartition (timeout-bounded session clear + dir removal).
• src/main/lib/ipc/sessionActions/delete.ts - call it on both delete paths, after record removal.
• src/main/lib/paths.ts - add selectedInstallDrive / defaultDataRoot / defaultDownloadCacheDir; system-drive Windows classifier (%LOCALAPPDATA%\Comfy-Desktop for new installs, home for existing) with a pinned marker via persistWinDataRootChoice; builtinDefaultInstallDir uses the data root.
• src/main/index.ts - call persistWinDataRootChoice() once at startup.
• src/main/settings.ts - default installDir, shared root, and download cache to the data root.

Tests

• delete.integration.test.ts - unique partition removed + session cleared; shared partition untouched; delete still completes when clearStorageData rejects; cleanup works when the install dir is already gone.
• paths.test.ts - drive redirect to <drive>\Comfy-Desktop on win32 non-home drive; system-drive new install -> %LOCALAPPDATA%\Comfy-Desktop; existing install (home footprint) -> home root + roaming cache; marker overrides later footprint changes in both directions; persistWinDataRootChoice writes the classified mode once and never overwrites; non-Windows unchanged.
• Full suite green: typecheck, lint, test (2053), integration (21), build.

[Kosinkadink]

Follow up - see if we can get the electron-manager userData moved as well.