feat(enhance): pick LoRAs from ComfyUI per job (#220)

Templates with `imageapi:lora-slot:<n>:high|low` nodes take LoRAs picked
per job from a catalog built live from ComfyUI.

- Catalog: ComfyUI's LoraLoaderModelOnly `lora_name` choices (cached
  60 s, re-read when a submit names an unknown id), paired by High/Low
  name tokens (StyleHigh/StyleLow, x-HIGH/x-LOW, x_high_noise/...). Files
  the workflow already loads outside the slots (lightx2v, switches) and
  `[template.catalog] exclude` substrings never show; ids derive from the
  names so they stay stable.
- POST /enhance `slots: [{lora, scale?}]` fills the slots in order: each
  pick sets the slot nodes' lora_name and scales their exported strength;
  unused slots run at 0, so the graph is never rewired. More picks than
  slots, duplicates or unknown ids are 400s.
- GET /enhance/templates gains `slots` and `catalog: {loras, strength,
  min, max}`; jobs store and return the picks (new enhance_jobs.lora_slots
  JSON column).

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

migrations/2026-11-03-200000_add_enhance_lora_slots/down.sql

@@ -0,0 +1 @@
+ALTER TABLE enhance_jobs DROP COLUMN lora_slots;

migrations/2026-11-03-200000_add_enhance_lora_slots/up.sql

@@ -0,0 +1,3 @@
+-- LoRAs picked into the template's slots (#220): JSON [{lora, label, scale}];
+-- NULL = none picked.
+ALTER TABLE enhance_jobs ADD COLUMN lora_slots TEXT;