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/modules/nfs/nfs.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"context"
 	"embed"
+	"encoding/json"
 	"fmt"
 	"os"
 	"path/filepath"
@@ -86,13 +87,62 @@ func (m *Module) Apply(ctx context.Context, database *db.DB) error {
 	return database.ClearDirty(ModuleName)
 }
 
-// clientSpec builds the "client(opts) client(opts)" segment of an exports line.
-// If no clients are configured, it defaults to "*(opts)".
-func clientSpec(clients []string, options string) string {
-	opts := strings.TrimSpace(options)
-	if opts == "" {
-		opts = "ro"
+func buildFlags(e db.NFSExport) string {
+	parts := make([]string, 0, 8)
+	if e.ReadOnly {
+		parts = append(parts, "ro")
+	} else {
+		parts = append(parts, "rw")
 	}
+	if e.Async {
+		parts = append(parts, "async")
+	} else {
+		parts = append(parts, "sync")
+	}
+	if e.SubtreeCheck {
+		parts = append(parts, "subtree_check")
+	} else {
+		parts = append(parts, "no_subtree_check")
+	}
+	if e.RootSquash {
+		parts = append(parts, "root_squash")
+	} else {
+		parts = append(parts, "no_root_squash")
+	}
+	if e.Advanced != "" && e.Advanced != "{}" {
+		var adv db.NFSAdvanced
+		if err := json.Unmarshal([]byte(e.Advanced), &adv); err == nil {
+			if adv.AllSquash {
+				parts = append(parts, "all_squash")
+			} else {
+				parts = append(parts, "no_all_squash")
+			}
+			if adv.Secure {
+				parts = append(parts, "secure")
+			} else {
+				parts = append(parts, "insecure")
+			}
+			if adv.WDelay {
+				parts = append(parts, "wdelay")
+			} else {
+				parts = append(parts, "no_wdelay")
+			}
+			if adv.Hide {
+				parts = append(parts, "hide")
+			} else {
+				parts = append(parts, "nohide")
+			}
+			if adv.Crossmnt {
+				parts = append(parts, "crossmnt")
+			}
+		}
+	}
+	parts = append(parts, fmt.Sprintf("fsid=%d", e.FSID))
+	return strings.Join(parts, ",")
+}
+
+func clientSpec(clients []string, e db.NFSExport) string {
+	opts := buildFlags(e)
 	if len(clients) == 0 {
 		return fmt.Sprintf("*(%s)", opts)
 	}
@@ -125,7 +175,7 @@ func (m *Module) renderConfig(exports []db.NFSExport) ([]byte, error) {
 	for _, export := range exports {
 		data.Exports = append(data.Exports, templateExport{
 			Path:       export.Path,
-			ClientSpec: clientSpec(export.Clients, export.Options),
+			ClientSpec: clientSpec(export.Clients, export),
 		})
 	}