admin: configure maintenance tasks via admin.toml (#9926)

* admin: configure maintenance tasks via admin.toml

Maintenance task settings could only be edited in the admin UI and live
under <dataDir>/conf, so they silently reverted to defaults whenever the
data directory was recreated. An optional admin.toml now declares vacuum,
balance, and erasure coding settings; keys set there are written through
to the persisted task configs at every startup, overriding UI edits, so
the configuration stays declarative. Generate an example with
"weed scaffold -config=admin".

* vacuum: round min volume age up to whole hours

MinVolumeAgeSeconds was truncated by integer division when converted to
the hour-granular protobuf field, so a sub-hour setting silently became
0 and disabled the age guard.

* admin: split and normalize preferred_tags from admin.toml

A comma-separated string, as set via environment variable, came through
viper as a single slice element. Split on commas and reuse
util.NormalizeTagList, matching the plugin config path.

* scaffold: clarify admin.toml wording

weed/command/admin.go

@@ -171,8 +171,17 @@ var cmdAdmin = &Command{
     - Metrics are disabled when -metricsPort is 0 (the default)
     - Example: weed admin -metricsPort=9327 -master="localhost:9333"
 
+  Maintenance Configuration:
+    - An optional admin.toml declares maintenance task settings
+      ([maintenance.vacuum], [maintenance.balance], [maintenance.erasure_coding])
+    - Settings in admin.toml are applied at every startup, overriding values
+      saved from the admin UI, so they can be managed declaratively
+    - Requires -dataDir; values can also be set via WEED_* environment
+      variables, e.g. WEED_MAINTENANCE_VACUUM_GARBAGE_THRESHOLD=0.3
+    - Generate example admin.toml: weed scaffold -config=admin
+
   Configuration File:
-    - The security.toml file is read from ".", "$HOME/.seaweedfs/",
+    - The security.toml and admin.toml files are read from ".", "$HOME/.seaweedfs/",
       "/usr/local/etc/seaweedfs/", or "/etc/seaweedfs/", in that order
     - Generate example security.toml: weed scaffold -config=security
 
@@ -191,6 +200,9 @@ func runAdmin(cmd *Command, args []string) bool {
 	// Load security configuration
 	util.LoadSecurityConfiguration()
 
+	// Optional admin.toml with maintenance task settings
+	util.LoadConfiguration("admin", false)
+
 	// Apply security.toml / env var fallbacks for credential flags.
 	// CLI flags take precedence over security.toml / WEED_* env vars.
 	applyViperFallback(cmd, a.adminUser, "adminUser", "admin.user")
@@ -337,6 +349,12 @@ func startAdminServer(ctx context.Context, options AdminOptions, enableUI bool,
 		glog.Infof("Data directory created/verified: %s", dataDir)
 	}
 
+	// Write maintenance task settings from admin.toml into the persisted
+	// task configs before the server loads them
+	if err := dash.NewConfigPersistence(dataDir).ApplyMaintenanceConfigFromToml(util.GetViper()); err != nil {
+		return fmt.Errorf("apply admin.toml: %w", err)
+	}
+
 	// Detect TLS configuration to set Secure cookie flag
 	cookieSecure := viper.GetString("https.admin.key") != ""