plugin worker: support job type categories (all, default, heavy) (#8547)

* plugin worker: add handler registry with job categories

Introduce a self-registration pattern for plugin worker job handlers.
Each handler can register itself via init() with a HandlerFactory that
declares its job type, category (default/heavy), CLI aliases, and a
builder function.

ResolveHandlerFactories accepts a mix of category names ("all",
"default", "heavy") and explicit job type names/aliases, returning the
matching factories. This enables workers to be configured by resource
profile rather than requiring explicit job type enumeration.

* plugin worker: register all handlers via init()

Each job handler now self-registers into the global handler registry
with its canonical job type, category, CLI aliases, and build function:

  - vacuum:              category=default
  - volume_balance:      category=default
  - admin_script:        category=default
  - erasure_coding:      category=heavy
  - iceberg_maintenance: category=heavy

Adding a new job type now only requires adding the init() call in the
handler file itself — no other files need to be touched.

* plugin worker: replace hardcoded job type switch with registry

Remove buildPluginWorkerHandler, parsePluginWorkerJobTypes, and
canonicalPluginWorkerJobType from worker_runtime.go. The simplified
buildPluginWorkerHandlers now delegates to
pluginworker.ResolveHandlerFactories, which resolves category names
("all", "default", "heavy") and explicit job type names/aliases.

The default job type is changed from an explicit list to "all", so new
handlers registered via init() are automatically picked up.

Update all tests to use the new API.

* plugin worker: update CLI help text for job categories

Update the -jobType flag description and command examples to document
category support (all, default, heavy) alongside explicit job type names.

* plugin worker: address review feedback

- Add CategoryAll constant; use typed constants in tokenAsCategory
- Pre-allocate result slice in ResolveHandlerFactories
- Add vacuum aliases (vol.vacuum, volume.vacuum)
- List alias examples (ec, balance, iceberg) in -jobType flag help
- Create handlers aggregator package for subpackage blank imports so
  new handler subpackages only need to be added in one place
- Make category tests relationship-based (subset/union checks) instead
  of asserting exact handler counts
- Add clarifying comments to worker_test.go and mini_plugin_test.go
  listing expected handler names next to count assertions

---------

Co-authored-by: Copilot <copilot@github.com>

weed/plugin/worker/admin_script_handler.go

@@ -33,6 +33,17 @@ s3.clean.uploads -timeAgo=24h`
 
 var adminScriptTokenRegex = regexp.MustCompile(`'.*?'|".*?"|\S+`)
 
+func init() {
+	RegisterHandler(HandlerFactory{
+		JobType:  "admin_script",
+		Category: CategoryDefault,
+		Aliases:  []string{"admin-script", "admin.script", "script", "admin"},
+		Build: func(opts HandlerBuildOptions) (JobHandler, error) {
+			return NewAdminScriptHandler(opts.GrpcDialOption), nil
+		},
+	})
+}
+
 type AdminScriptHandler struct {
 	grpcDialOption grpc.DialOption
 }