decide() DSL hardcodes value-param evaluator — JavaScript evaluator unreachable

## Summary

The `decide()` DSL method hardcodes `evaluator_type = 'value-param'` for all SWITCH tasks. Users who need a JavaScript expression evaluator must construct `WorkflowTask` manually — there is no way to express this through the builder.

Tested against: **Conductor OSS 3.32.0-rc.9**

## Root Cause

```ruby
# lib/conductor/workflow/dsl/task_ref.rb:110-111
def apply_switch_fields(wf_task)
wf_task.evaluator_type = 'value-param' # hardcoded — cannot be 'javascript'
...
end
```

`workflow_builder.rb#add_switch_task` passes no `evaluator_type` in options; `apply_switch_fields` ignores any such option and hardcodes `'value-param'`.

The server supports two evaluator types for SWITCH:
- `"value-param"` — compares `inputParameters.switchCaseValue` against case strings
- `"javascript"` — evaluates a full JavaScript expression and matches the result against cases

## Impact

Users who want to branch on a computed value (not a simple reference comparison) cannot use the `decide` DSL. They must construct the task definition raw.

## Fix

Thread `evaluator_type` through from `decide()`:

```ruby
# workflow_builder.rb
def decide(expression, evaluator_type: 'value-param', &block)
builder = SwitchBuilder.new(resolve_value(expression), self)
builder.instance_eval(&block)
add_switch_task(builder, evaluator_type: evaluator_type)
end

def add_switch_task(builder, evaluator_type: 'value-param')
task_ref = TaskRef.new(
...
options: {
expression: builder.expression,
evaluator_type: evaluator_type, # ← pass through
decision_cases: builder.cases,
default_case: builder.default
}
)
...
end

# task_ref.rb
def apply_switch_fields(wf_task)
wf_task.evaluator_type = @options[:evaluator_type] || 'value-param'
...
end
```

Related: JavaScript SDK [#139](https://github.com/conductor-oss/javascript-sdk/issues/139) — same gap.

Read lib/conductor/workflow/dsl/task_ref.rb at apply_switch_fields and workflow_builder.rb at decide and add_switch_task. Trace how switch options reach WorkflowTask, then verify that the default remains value-param and that selecting javascript produces the corresponding evaluator type for the built SWITCH task.

Written by the indexing model from the issue text.