docs: improve skill documentation clarity

- Fix Provider Selection: default to Replicate when multiple keys available (matches code)
- Add Replicate column to Quality Presets table (normal→1K, 2k→2K)
- Add Replicate aspect ratio behavior (match_input_image when --ref without --ar)
- Remove stale Google Imagen reference from Aspect Ratios
- Add batch file format example with JSON schema to SKILL.md
- Note that batch paths resolve relative to batch file directory
- Move batch execution strategy in article-illustrator before numbered steps
- Fix translate image-language reminder to use standard markdown syntax
  with note to match article's own image syntax convention

skills/baoyu-article-illustrator/references/workflow.md

@@ -315,6 +315,10 @@ Prompt Files:
 
 **DO NOT** pass ad-hoc inline text to `--prompt` without first saving prompt files. The generation command should either use `--promptfiles prompts/NN-{type}-{slug}.md` or read the saved file content for `--prompt`.
 
+**Execution choice**:
+- If multiple illustrations already have saved prompt files and the task is now plain generation, prefer `baoyu-image-gen` batch mode (`build-batch.ts` -> `main.ts --batchfile`)
+- Use subagents only when each illustration still needs separate prompt rewriting, style exploration, or other per-image reasoning before generation
+
 **CRITICAL - References in Frontmatter**:
 - Only add `references` field if files ACTUALLY EXIST in `references/` directory
 - If style/palette was extracted verbally (no file), append info to prompt BODY instead