feat: add storage info to settings page and improve NFS export handling

Backend:
- Add source/used_by/available/error fields to diskUsage in system status
- collectDiskUsage() now reads /proc/mounts, samba shares and NFS exports from DB
- Paths are deduplicated; shared paths list all shares/exports using them
- syscall.Statfs errors surface as available=false with user-facing error
- collectServiceStatus made a method of Server (receiver consistency)

Frontend:
- Settings page now shows two cards: mount points and shared resources
- Each path shows source badge (Sistema/Mount/SMB/NFS), used_by chips, progress bar
- Unavailable paths show amber warning instead of progress bar
- DiskUsage interface updated with new fields
- NFSExport interface updated with structured fields (fsid, async, etc)
- NFS page updated to use new export fields

internal/db/queries_import.go

@@ -61,10 +61,30 @@ func (d *DB) ReplaceNFSExports(exports []NFSExport) error {
 		if err != nil {
 			return err
 		}
+		readOnly := 0
+		if exp.ReadOnly {
+			readOnly = 1
+		}
+		async_ := 0
+		if exp.Async {
+			async_ = 1
+		}
+		rootSquash := 0
+		if exp.RootSquash {
+			rootSquash = 1
+		}
+		subtreeCheck := 0
+		if exp.SubtreeCheck {
+			subtreeCheck = 1
+		}
+		advanced := exp.Advanced
+		if advanced == "" {
+			advanced = "{}"
+		}
 		_, err = tx.Exec(`
-			INSERT INTO nfs_exports (path, clients, options)
-			VALUES (?, ?, ?)`,
-			exp.Path, clients, exp.Options,
+			INSERT INTO nfs_exports (path, clients, read_only, async_, root_squash, subtree_check, fsid, advanced)
+			VALUES (?, ?, ?, ?, ?, ?, ?, ?)`,
+			exp.Path, clients, readOnly, async_, rootSquash, subtreeCheck, exp.FSID, advanced,
 		)
 		if err != nil {
 			return fmt.Errorf("insert nfs export %s: %w", exp.Path, err)