fix(ec): bring ec.encode worker and EC/volume helpers to parity with shell (#9599)

* refactor(volume): extract replica sync/select into shared volume_replica package

Move the volume replica reconciliation helpers (status, union builder,
SyncAndSelectBestReplica, ReadNeedleMeta) out of the shell into a new
weed/storage/volume_replica package so both the shell (ec.encode, volume.tier.move,
volume.check.disk) and the EC encode worker can reuse them. No behavior change.

* fix(ec): bring ec.encode worker to parity with the shell

- Sync replicas and encode the most-complete one (via the shared
  volume_replica.SyncAndSelectBestReplica) instead of a possibly-stale replica,
  marking all replicas readonly first. Prevents silent data loss when a stale
  replica is encoded and the originals deleted.
- Skip remote/tiered volumes in detection (shell ec.encode excludes them).
- Min-node safety gate: refuse to encode when cluster nodes < parity shards.
- Align default thresholds with the shell (fullness 0.95, quiet 1h).

* fix(vacuum): plugin path honors min_volume_age_seconds override

deriveVacuumConfig hard-coded MinVolumeAgeSeconds=0, dropping any configured
value. Read it from worker config (default 0, matching the shell/master vacuum
which has no age gate) so an explicit override is honored.

* address review feedback

- config.go: align GetConfigSpec schema defaults (quiet_for_seconds=3600,
  fullness_ratio=0.95) with the runtime defaults so UI/bootstrap flows match the
  shell (coderabbitai).
- ec_task.go: roll back readonly when markReplicasReadonly fails partway, so
  already-marked replicas don't stay readonly (coderabbitai).
- volume_replica: pass the caller's replica statuses into buildUnionReplica instead
  of re-fetching them, and skip the per-needle ReadNeedleMeta RPC when the source
  replica is read-only (gemini-code-assist).

* test(plugin_workers/ec): make fixtures eligible under the new defaults

The default EC encode thresholds were raised to match the shell (fullness 0.95,
quiet 1h), but the plugin-worker integration fixtures still used 90%-full /
10-minute-old volumes, so detection found no eligible volumes and the tests failed
in CI. Bump the eligible fixtures to 96% full and 2h old.

weed/worker/tasks/erasure_coding/plugin_handler.go

@@ -143,10 +143,10 @@ func (h *ErasureCodingHandler) Descriptor() *plugin_pb.JobTypeDescriptor {
 			},
 			DefaultValues: map[string]*plugin_pb.ConfigValue{
 				"quiet_for_seconds": {
-					Kind: &plugin_pb.ConfigValue_Int64Value{Int64Value: 300},
+					Kind: &plugin_pb.ConfigValue_Int64Value{Int64Value: 3600},
 				},
 				"fullness_ratio": {
-					Kind: &plugin_pb.ConfigValue_DoubleValue{DoubleValue: 0.8},
+					Kind: &plugin_pb.ConfigValue_DoubleValue{DoubleValue: 0.95},
 				},
 				"min_size_mb": {
 					Kind: &plugin_pb.ConfigValue_Int64Value{Int64Value: 30},
@@ -170,10 +170,10 @@ func (h *ErasureCodingHandler) Descriptor() *plugin_pb.JobTypeDescriptor {
 		},
 		WorkerDefaultValues: map[string]*plugin_pb.ConfigValue{
 			"quiet_for_seconds": {
-				Kind: &plugin_pb.ConfigValue_Int64Value{Int64Value: 300},
+				Kind: &plugin_pb.ConfigValue_Int64Value{Int64Value: 3600},
 			},
 			"fullness_ratio": {
-				Kind: &plugin_pb.ConfigValue_DoubleValue{DoubleValue: 0.8},
+				Kind: &plugin_pb.ConfigValue_DoubleValue{DoubleValue: 0.95},
 			},
 			"min_size_mb": {
 				Kind: &plugin_pb.ConfigValue_Int64Value{Int64Value: 30},