Add asset creation skill and artist agent for Stickman Studio

- Introduced a new artist agent to create and review vector, raster, clothing, prop, and animation assets based on user prompts or reference images.
- Created an asset-creation skill to manage the delegation, review, approval, and handoff processes for graphical assets and animations.
- Added project format routing documentation to guide asset creation and ensure consistency in Stickman Studio.
- Established a review workflow for asset promotion, ensuring thorough validation and user approval before finalizing assets.
- Documented the specifications for scenery, backgrounds, and vector surface finishes to enhance the child experience in the Sandbox Stage.

.codex/skills/spec-pipeline/SKILL.md

@@ -30,8 +30,16 @@ description: "Stickman Studio feature workflow: UI/UX and architecture specs, im
    - The spec states observable acceptance outcomes and the user path that produces each one. For interactions involving physics, timing, saving/loading, or multiple systems, name a small repeatable runtime scenario and what to measure; do not prescribe a test implementation unless it is needed to protect a specific behavior.
    - **STOP:** Wait for final user sign-off on the spec before invoking developer.
 
-5. **Phase 2: Implementation & Agent Verification**
+5. **Phase 1c: Conditional Art Production & Approval**
+   - After spec sign-off, inspect the accepted specification for explicit new graphical or animation deliverables. Skip this phase when none are required.
+   - Invoke `$asset-creation`, which delegates to `@artist`, with the signed-off specification, supplied reference images, intended asset type, and integration constraints.
+   - `@artist` creates validated candidates under `content/review/artist/<request-slug>/`, including a preview and `review.md`; it does not modify gameplay/runtime architecture or promote the candidates yet.
+   - Present the review bundle and **STOP** for user approval or revision. Do not invoke developer while required artwork remains unapproved.
+   - After explicit approval, promote the selected assets to their production locations and pass their paths plus integration notes to developer.
+
+6. **Phase 2: Implementation & Agent Verification**
    - `@developer` updates code and scenes using targeted diffs based on `docs/specs/[feature-name].md`.
+   - When Phase 1c ran, `@developer` consumes the approved asset paths and Artist integration notes; it does not silently replace approved artwork.
    - `@developer` runs Godot syntax/import checks and focused existing regression suites, then fixes failures.
    - `@developer` adds focused automated coverage where it can meaningfully verify the feature's observable acceptance outcomes. For cross-system or runtime behavior, construct a small repeatable scene or fixture (in memory or as a saved scene), use the real production spawning/input/action paths where practical, advance frames or physics ticks, and assert the resulting state. A check that nodes, signals, layers, or helper calls exist is insufficient when the requirement concerns what actually happens during play.
    - For visual or interactive acceptance criteria, establish the verification route before concluding Phase 2: run the affected scene in a render-capable GUI session, capture the states named in the spec, and inspect the rendered pixels. Record the scene/state, capture location, and what was observed. A successful launch, headless run, or screenshot command/file by itself does not prove visual correctness.
@@ -39,8 +47,8 @@ description: "Stickman Studio feature workflow: UI/UX and architecture specs, im
    - If the environment may not support rendering or input, try to establish whether a GUI, capture, or input-automation route is available; do not infer that it is unavailable from a headless run alone. If verification still cannot be performed, record what was attempted and the specific limitation, mark the affected acceptance outcomes unverified, and leave a focused, reproducible user check. Do not report the feature as fully agent-verified while required outcomes remain unverified.
    - `@developer` reruns the relevant checks after fixes and reports commands, pass/fail results, the measured behavior, and any unverified acceptance outcome. Do not claim a feature is verified from syntax checks or debug prints alone.
 
-6. **Phase 3: User Hand-off (Stop)**
+7. **Phase 3: User Hand-off (Stop)**
    - Present the implementation and agent verification evidence. Give the user only the remaining visual, usability, or environment-dependent checks to perform in the Godot Editor; clearly identify any acceptance outcome the agent could not verify.
 
-7. **Phase 4: Documentation (Triggered manually by user)**
+8. **Phase 4: Documentation (Triggered manually by user)**
    - Only call `@writer` after the user confirms: "Feature verified and working."