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/asset-creation/SKILL.md

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+---
+name: asset-creation
+description: "Create or revise Stickman Studio props, stickmen, embedded clothing, PNG art, or character/prop animation by orchestrating the Artist and an explicit review-and-approval workflow."
+---
+
+# Asset Creation
+
+Use the `artist` subagent for project graphical-asset and animation work. This skill manages delegation, review, approval, and handoff; it does not replace the Artist's visual judgment.
+
+## Delegate to Artist
+
+Spawn `artist` with `agent_type: "artist"`. Reuse the same Artist for revisions while it is available. Tell it that other agents may share the workspace and that it must preserve unrelated changes.
+
+Pass the user's request, intended use, supplied image roles (reference versus edit target), relevant approved specification, requested format, and any style or technical constraints. Do not require the user to repeat information already available in the conversation or repository.
+
+Before delegating, read [references/project-formats.md](references/project-formats.md) for routing and source-of-truth locations. For production or revision work, also read [references/review-workflow.md](references/review-workflow.md).
+
+## Choose the deliverable path
+
+- Prefer native `.prop` or `.stk` for project line art that must remain editable and compatible with the existing editors/runtime.
+- Treat clothing as layered shapes embedded in affected `.stk` body parts. A reusable or swappable wardrobe is a separate feature requiring design and architecture work.
+- For requested bitmap art, have Artist use the `imagegen` skill and move project-bound results into its review bundle.
+- For animation, use the current rig and authoring representation. Do not create a new prop-animation schema merely to fulfill an asset request.
+- Artist may browse for supporting visual references without a separate confirmation. It must record source URLs and must not redistribute unlicensed reference art.
+
+## Review before promotion
+
+Artist writes unapproved work to `content/review/artist/<request-slug>/`. Present the preview, candidate paths, suggestions, and validation results to the user, then stop for approval or revision.
+
+Approval to create a draft is not approval to overwrite or promote a production asset. Promote only after explicit approval, preserve rejected variants until cleanup is requested, and use a versioned production filename unless replacement was explicitly requested.
+
+When implementation work is also needed, hand the approved asset paths and `review.md` integration notes to `developer`. Artist must not absorb gameplay, editor, serializer, or runtime architecture work.

.codex/skills/asset-creation/agents/openai.yaml

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+interface:
+  display_name: "Asset Creation"
+  short_description: "Create and review Stickman Studio artwork"
+  default_prompt: "Use $asset-creation to create a review-ready Stickman Studio asset from my description or reference image."

.codex/skills/asset-creation/references/project-formats.md

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+# Project asset format routing
+
+Inspect these sources at execution time; do not copy their schemas into prompts because the formats evolve.
+
+## Stickmen and embedded clothing
+
+- Serializer and current version: `scripts/editors/stickman/stickman_editor.gd`
+- Runtime conversion: `scripts/characters/stickman/stk_rig_adapter.gd`
+- Rig target: `scenes/characters/stickman/stickman_rig.tscn`
+- Representative current assets: `content/stickmen/*.stk` (confirm the version before choosing a sample)
+- Visual harness: `scenes/tools/test_harness.tscn`
+
+An `.stk` owns ten body-part records and may contain multiple layered shapes per part. Clothing uses those layers until the project defines a separate wardrobe format. Preserve joint alignment, guide offsets, pivots, length metadata, body-part transforms, shape ordering, and the serializer's current version contract.
+
+## Props
+
+- Serializer/parser: `scripts/editors/prop/prop_file.gd`
+- Anchor normalization: `scripts/props/prop_anchor_data.gd`
+- Runtime visual/collision interpretation: `scripts/props/prop_visuals.gd`
+- Representative assets: `content/props/*.prop`
+- Visual editor: `scenes/editors/prop/prop_editor.tscn`
+
+Use current `PropFile` output, including shape styling and normalized anchors. Ensure at least one valid closed shape can provide runtime collision geometry when the prop is intended for stage use. Lines are visual/editor shapes and do not supply collision geometry.
+
+## Animation
+
+- Rig scene: `scenes/characters/stickman/stickman_rig.tscn`
+- Existing authoring tool: `scripts/tools/create_animations.gd`
+- Playback behavior: inspect the relevant component under `scripts/characters/stickman/`
+
+Stickman animations target the current rig's IK or animation targets, not `.stk` shape coordinates. Match the runtime clip name and locomotion/facing contract from the approved specification. For animated props, use only a representation already defined by the feature; otherwise return art direction, states, and timing requirements for architecture.
+
+## PNG art
+
+Use the `imagegen` skill for generated or edited raster art. Preserve alpha when transparency is requested. Approved PNGs go into the narrowest fitting `resources/` category; create a new `resources/art/<feature-or-kind>/` folder only if no current category fits.

.codex/skills/asset-creation/references/review-workflow.md

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+# Asset review and promotion
+
+## Review bundle
+
+Use `content/review/artist/<request-slug>/`, where the slug is short, lowercase, and hyphenated. This tree is ignored by Git and is not scanned by the immediate-child prop and stickman library scanners.
+
+Keep:
+
+- versioned candidate files such as `briefcase-v1.prop` or `detective-coat-v2.stk`;
+- `preview.png` or a clearly named contact sheet;
+- animation key-pose captures when applicable;
+- `review.md`.
+
+`review.md` records:
+
+- the requested outcome and intended use;
+- which supplied images were references and which, if any, were edit targets;
+- creative choices and optional Artist suggestions;
+- external reference URLs and known license/usage notes;
+- candidate filenames and intended production destinations;
+- validation commands or scenes, observed results, and unverified outcomes.
+
+Do not copy browsed reference images into the bundle unless the user owns them or their license permits redistribution.
+
+## Approval boundary
+
+Show the preview and report the candidate paths. Wait for explicit approval before copying a candidate to a production location. Revision requests produce a new version rather than destroying the earlier candidate.
+
+After approval:
+
+- `.prop` -> `content/props/`
+- `.stk` -> `content/stickmen/`
+- PNG -> the relevant existing `resources/` category, or `resources/art/<kind>/` when necessary
+- animation -> the approved specification's rig/tool asset location
+
+Never overwrite an existing production file unless the user specifically approves replacement. Do not delete the review bundle unless the user asks for cleanup.