App storage quota warning removed (disk-space warning retained)

What changed

The browser storage-quota warning (triggered when navigator.storage usage reached ≥95%) has been removed. The data-directory low-disk warning (free space < 1 GiB) is retained — it now runs in the main process and auto-dismisses once space is freed.

Why this matters to the user

In v1 the storage-quota warning watched the renderer's browser storage (redux-persist and friends). Since v2 keeps business data in the main-process SQLite database, that quota no longer reflects where data is actually stored, so the warning was misleading and is gone. Users will no longer see an "app storage quota" warning, but they are still warned when the disk that holds their data is genuinely running out of space.

What the user should do

Nothing — automatic. Disk protection is retained and improved: the low-space notification now appears reliably and clears itself once space is freed.

Notes for release manager

The removed piece is the checkAppStorageQuota check only. The retained disk-space check moved from a renderer-side timer to the main-process StorageMonitorService (capacity-adaptive polling, main window only, auto-dismiss); the warning threshold is unchanged at free space < 1 GiB. Set introduced_in_pr to the actual PR number on merge.