feat(enhance): LoRA strength scale alongside the on/off switch (#218)

So the app builds against the final shape: each [[template.lora]] gains
`strength` (the scale when on, default 1.0) and `min` / `max` (the
slider's range, default 0.0-1.5).

- POST /enhance `loras` takes true / false or a scale: true = strength,
  false or <= 0 = off, a scale is clamped to min..max.
- The scale multiplies each node's exported strength_model /
  strength_clip, so 1.0 = as exported and a high/low pair keeps its
  ratio.
- Jobs and the job view store the resolved scale per id (0 = off);
  GET /enhance/templates lists strength, min and max.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/enhance/service.rs

@@ -292,7 +292,7 @@ impl EnhanceService {
         template_name: &str,
         prompt: Option<&str>,
         reference: Option<&SourceFile>,
-        loras: &std::collections::BTreeMap<String, bool>,
+        loras: &std::collections::BTreeMap<String, super::config::LoraRequest>,
     ) -> Result<EnhanceJobRow, EnhanceError> {
         let Some(client) = &self.client else {
             return Err(EnhanceError::Disabled);