docs(baoyu-article-illustrator,baoyu-comic,baoyu-infographic,baoyu-slide-deck,baoyu-xhs-images): point codex-imagegen flow at baoyu-image-gen --provider codex-cli

Add a `Codex via codex exec` branch to each skill's backend-selection
ladder and ship a per-skill references/codex-imagegen.md with the
invocation contract (preferred baoyu-image-gen --provider codex-cli
path, direct-wrapper fallback, parameter notes, stdout schema, batch
semantics).

skills/baoyu-comic/SKILL.md

@@ -1,7 +1,7 @@
 ---
 name: baoyu-comic
 description: Knowledge comic creator supporting multiple art styles and tones. Creates original educational comics with detailed panel layouts and batch-capable image generation. Use when user asks to create "知识漫画", "教育漫画", "biography comic", "tutorial comic", or "Logicomix-style comic".
-version: 1.117.3
+version: 1.117.4
 metadata:
   openclaw:
     homepage: https://github.com/JimLiu/baoyu-skills#baoyu-comic
@@ -33,6 +33,7 @@ When this skill needs to render an image, resolve the backend in this order:
 2. **Saved preference** — if `EXTEND.md` sets `preferred_image_backend` to a backend available right now, use it.
 3. **Auto-select** (when the preference is `auto`, unset, or the pinned backend isn't available):
    - **Codex (`imagegen`)** — first, inspect your available-skills / tool inventory. If a skill named `imagegen` is listed, you are running inside Codex and MUST use it: invoke via the `Skill` tool with `skill: "imagegen"`, passing the saved prompt file's content (plus output path and aspect ratio per Codex `imagegen`'s own args). Codex `imagegen` is the official raster backend in that runtime and outranks any non-native skill (e.g., `baoyu-image-gen`) unless the user has explicitly pinned a different `preferred_image_backend`.
+   - **Codex via `codex exec` (`codex-imagegen`)** — if the current runtime exposes no native `imagegen` skill but the `codex` CLI is on `PATH` with an active `codex login`, route through `baoyu-image-gen --provider codex-cli` (preferred), or — if baoyu-image-gen is unavailable — invoke the bundled wrapper directly. Details, parameters, and the runtime-discovery procedure live in [references/codex-imagegen.md](references/codex-imagegen.md) — load that file only when this branch is selected.
    - **Other runtime-native tools** — if the runtime exposes a different native image tool (e.g., Hermes `image_generate`), use it the same way.
    - Otherwise, if exactly one non-native backend is installed (e.g., `baoyu-image-gen`), use it.
    - Otherwise (multiple non-native backends with no runtime-native tool), ask the user once — batch with any other initial questions.
@@ -247,6 +248,8 @@ Analyze → [Check Existing?] → [Confirm: Style + Reviews] → Storyboard →
 
 **Pick a backend once per session** using the `## Image Generation Tools` rule at the top. If the backend is a repo skill (e.g., `baoyu-image-gen`), read its `SKILL.md` and use its documented interface rather than its scripts.
 
+**`codex-imagegen` invocation**: when the rule resolves to `codex-imagegen`, see [references/codex-imagegen.md](references/codex-imagegen.md) for the invocation contract (preferred `baoyu-image-gen --provider codex-cli` path, runtime wrapper discovery, parameter notes, stdout schema, batch semantics — n=1 per call so page batches must dispatch one wrapper call per page).
+
 **7.1 Character sheet** — generate it (to `characters/characters.png`, aspect `4:3`) when the comic is multi-page with recurring characters. Skip for simple presets (e.g., four-panel minimalist) or single-page comics. Compress to JPEG before use-as-`--ref` (`sips -s format jpeg -s formatOptions 80 …` on macOS, `pngquant --quality=65-80 …` elsewhere) to avoid payload failures. The prompt file at `characters/characters.md` must exist before invoking the backend.
 
 **7.2 Pages** — each page's prompt MUST already be at `prompts/NN-{cover|page}-[slug].md` before invoking the backend; the file is the reproducibility record. Strategy depends on the character sheet: