fix(scheduler): give worker tasks a real per-attempt execution deadline (#9041)

* fix(scheduler): give worker tasks a real per-attempt execution deadline

The plugin scheduler derived the per-attempt execution deadline as
DetectionTimeoutSeconds * 2, which capped every worker task at twice
the cluster-scan budget regardless of actual work. For volume_balance
batches this was 240s — far too short for 20 large volume copies, so
every attempt died at "context deadline exceeded" and all in-flight
sub-RPCs surfaced as "context canceled". Retries restarted from move 1
and hit the same wall.

Add an explicit ExecutionTimeoutSeconds field to the plugin proto and
make each handler declare its own baseline (1800s for vacuum, balance,
EC; 3600s for iceberg). Size-aware handlers also emit an
estimated_runtime_seconds parameter on each proposal so the scheduler
extends the per-attempt deadline based on actual workload:

- volume_balance batch: max(largest single move, total / concurrency)
  at 5 min/GB, so a skewed batch with one big volume isn't averaged
  away.
- volume_balance single, vacuum (already), erasure_coding (10 min/GB),
  ec_balance (5 min/GB): per-volume budgets.

admin_script and iceberg keep the configurable handler default since
their workloads are opaque to the detector.

* fix(scheduler): apply descriptor defaults to existing persisted configs

The previous commit added execution_timeout_seconds to the proto and
each handler's descriptor defaults, but two paths still left existing
deployments broken:

1. deriveSchedulerAdminRuntime returned stored AdminRuntime configs
   as-is. Persisted configs from older versions have no
   execution_timeout_seconds, so the scheduler fell back to the 90s
   default — worse than the prior 240s behavior. Overlay descriptor
   defaults for any zero numeric fields when loading.

2. The admin form did not round-trip execution_timeout_seconds, so a
   normal save would clear it back to zero. Add the input field, the
   fillAdminSettings/collectAdminSettings hooks, and as defense in
   depth reapply descriptor defaults in UpdatePluginJobTypeConfigAPI
   before persisting so a stale form can never silently clobber a
   baseline.

* fix(volume_balance): account for partial scheduling rounds in batch estimate

With N moves and C slots, the busiest slot processes ceil(N/C) moves,
not N/C. Dividing total seconds by C underestimates wall-clock time
whenever N is not a multiple of C — e.g. 6 moves at concurrency 5
needs 2 rounds, not 1.2. Use avg * ceil(N/C) so partial rounds are
counted as full ones.

* fix(volume_balance): scale minBudget per wave instead of per move

Orchestration overhead (setup/teardown for the parallel move runner)
happens once per wave, not once per move. Use numRounds*60 as the
floor instead of len(moves)*60 so the minimum doesn't inflate
linearly with batch size when individual moves are tiny.

weed/admin/view/app/plugin.templ

@@ -266,6 +266,11 @@ templ Plugin(page string, initialJob string, lane string) {
                                     <label class="form-label" for="plugin-admin-detection-timeout">Detection Timeout (s)</label>
                                     <input type="number" class="form-control" id="plugin-admin-detection-timeout" min="0"/>
                                 </div>
+                                <div class="col-12">
+                                    <label class="form-label" for="plugin-admin-execution-timeout">Execution Timeout (s)</label>
+                                    <input type="number" class="form-control" id="plugin-admin-execution-timeout" min="0"/>
+                                    <div class="form-text">Per-attempt deadline for one job. Size-aware tasks may extend this automatically.</div>
+                                </div>
                                 <div class="col-12">
                                     <label class="form-label" for="plugin-admin-max-runtime">Job Type Max Runtime (s)</label>
                                     <input type="number" class="form-control" id="plugin-admin-max-runtime" min="0"/>
@@ -2519,6 +2524,7 @@ templ Plugin(page string, initialJob string, lane string) {
                 document.getElementById('plugin-admin-enabled').checked = pickBool('enabled');
                 document.getElementById('plugin-admin-detection-interval').value = String(pickNumber('detection_interval_seconds'));
                 document.getElementById('plugin-admin-detection-timeout').value = String(pickNumber('detection_timeout_seconds'));
+                document.getElementById('plugin-admin-execution-timeout').value = String(pickNumber('execution_timeout_seconds'));
                 document.getElementById('plugin-admin-max-runtime').value = String(pickNumber('job_type_max_runtime_seconds'));
                 document.getElementById('plugin-admin-max-results').value = String(pickNumber('max_jobs_per_detection'));
                 document.getElementById('plugin-admin-global-exec').value = String(pickNumber('global_execution_concurrency'));
@@ -2544,6 +2550,7 @@ templ Plugin(page string, initialJob string, lane string) {
                     enabled: !!document.getElementById('plugin-admin-enabled').checked,
                     detection_interval_seconds: getInt('plugin-admin-detection-interval'),
                     detection_timeout_seconds: getInt('plugin-admin-detection-timeout'),
+                    execution_timeout_seconds: getInt('plugin-admin-execution-timeout'),
                     job_type_max_runtime_seconds: getInt('plugin-admin-max-runtime'),
                     max_jobs_per_detection: getInt('plugin-admin-max-results'),
                     global_execution_concurrency: getInt('plugin-admin-global-exec'),