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/fsid.go

@@ -0,0 +1,32 @@
+package nfs
+
+import (
+	"crypto/rand"
+	"encoding/binary"
+	"fmt"
+)
+
+func generateRandomFSID() (uint32, error) {
+	var b [4]byte
+	if _, err := rand.Read(b[:]); err != nil {
+		return 0, fmt.Errorf("crypto/rand read: %w", err)
+	}
+	n := binary.BigEndian.Uint32(b[:])
+	if n == 0 {
+		n = 1
+	}
+	return n, nil
+}
+
+func UniqueFSID(used map[uint32]struct{}) (uint32, error) {
+	for i := 0; i < 64; i++ {
+		n, err := generateRandomFSID()
+		if err != nil {
+			return 0, err
+		}
+		if _, dup := used[n]; !dup {
+			return n, nil
+		}
+	}
+	return 0, fmt.Errorf("fsid space exhausted after 64 attempts")
+}

internal/modules/nfs/fsid_test.go

@@ -0,0 +1,56 @@
+package nfs
+
+import (
+	"sync"
+	"testing"
+)
+
+func TestUniqueFSIDNoCollision(t *testing.T) {
+	const goroutines = 100
+	results := make(chan uint32, goroutines)
+	var wg sync.WaitGroup
+
+	for i := 0; i < goroutines; i++ {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			n, err := generateRandomFSID()
+			if err != nil {
+				t.Errorf("generateRandomFSID failed: %v", err)
+				return
+			}
+			results <- n
+		}()
+	}
+
+	wg.Wait()
+	close(results)
+
+	seen := make(map[uint32]struct{})
+	for n := range results {
+		if _, dup := seen[n]; dup {
+			t.Errorf("duplicate fsid generated: %d", n)
+		}
+		seen[n] = struct{}{}
+	}
+}
+
+func TestUniqueFSIDWithUsedSet(t *testing.T) {
+	used := map[uint32]struct{}{
+		1: {}, 2: {}, 3: {},
+	}
+
+	for i := 0; i < 50; i++ {
+		n, err := UniqueFSID(used)
+		if err != nil {
+			t.Fatalf("UniqueFSID failed at iteration %d: %v", i, err)
+		}
+		if n == 0 {
+			t.Fatalf("fsid 0 is reserved")
+		}
+		if _, dup := used[n]; dup {
+			t.Fatalf("returned duplicate fsid: %d", n)
+		}
+		used[n] = struct{}{}
+	}
+}

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),
 		})
 	}