fix: P0+P1 critical bug fixes across controller (24 files)

Concurrency fixes:
- Deep-copy stacks in GetStack/GetStacks to prevent shared state mutation (C04)
- Add per-state mutex to watchdog pathProbeState (C05)
- Guard MetricsCollector.Start() with sync.Once against double-start (C06)
- Hold diskJobMu across entire raw mount operation (C07)
- Add mutex to SetEncryptionKey (C08), MigrateEncryption write lock (H03)
- Use sync.Once for sync.Stop() channel close (H08)
- Set syncing=true before releasing lock in TriggerSync (H09)
- Deep-copy lastDBDump/lastBackup in GetFullStatus (H11)
- Add WaitGroup for stderr goroutine in MigrateDrive (H19)
- Add mutex to SetBackupRunningCheck (M18)

Security fixes:
- Validate Bearer token against Hub API key in CSRF middleware (H16)
- Validate backup paths start with expected prefix in RemoveStack (M12)
- Guard uuid[:8] slice with length check (H20)
- Parse fstab fields exactly for mount target matching (H21)

Bug fixes:
- Use decrypted env vars for compose deploy (C01)
- Log decrypt failures in DecryptMap instead of swallowing (C02)
- Move Deployed=false inside lock in runComposeDeploy (C03)
- Fix activeDrives() to skip disconnected drives (H02)
- Fix Snapshot() stderr extraction from exec.ExitError (H01)
- Check unlockCmd.Run() error in restic (H01)
- Buffer template rendering via bytes.Buffer (H07)
- Thread context.Context through cloudflare client (H10)
- Fix leaf-name collision detection in cross-drive backup (H15)
- Add nil check for crossDriveRunner (H17)
- Use strings.TrimSpace instead of slice on command output (H18)
- Make SaveAppConfig atomic with write-to-tmp+rename (H04)
- Pass encKey on deploy failure SaveAppConfig (H05)
- Fix IPv6 address format in TCP health probe

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

controller/internal/crypto/crypto.go

@@ -7,6 +7,7 @@ import (
 	"crypto/rand"
 	"encoding/base64"
 	"fmt"
+	"log"
 	"os"
 	"strings"
 )
@@ -98,6 +99,7 @@ func IsEncrypted(value string) bool {
 }
 
 // DecryptMap decrypts all encrypted values in a map, returning a new map with plaintext values.
+// Logs a warning for any value that fails to decrypt (key rotation, data corruption).
 func DecryptMap(key []byte, env map[string]string) map[string]string {
 	if key == nil || env == nil {
 		return env
@@ -105,10 +107,14 @@ func DecryptMap(key []byte, env map[string]string) map[string]string {
 	result := make(map[string]string, len(env))
 	for k, v := range env {
 		if IsEncrypted(v) {
-			if dec, err := Decrypt(key, v); err == nil {
-				result[k] = dec
+			dec, err := Decrypt(key, v)
+			if err != nil {
+				log.Printf("[WARN] Failed to decrypt env var %q: %v — passing through encrypted value", k, err)
+				result[k] = v
 				continue
 			}
+			result[k] = dec
+			continue
 		}
 		result[k] = v
 	}