Add multi-platform export generator (single source of truth)

Make the library multi-platform without duplicating content. Each
skills/<name>/SKILL.md body remains the single source of truth; a new
generator renders platform-ready exports from it.

- scripts/build-exports.mjs — dependency-free Node generator with a PLATFORMS
  registry so new platforms (Gemini, Cursor, …) are a few lines. Ships ChatGPT
  exports at exports/chatgpt/<bundle>/<skill>/SYSTEM_PROMPT.md (172 skills),
  plus generated index READMEs. Supports --platform and --check.
- exports/ — generated ChatGPT system prompts, ready to paste into a Custom GPT.
- .github/workflows/check-generated.yml — fails a PR if exports or
  web/skills.json drift from the source skills.
- README "Works With" now documents the ready-to-use exports and regen command.
- CHANGELOG + SKILL-AUTHORING-STANDARD note the generated artifacts.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016JWn5jRD5tcEFKrubjQ6Px

exports/chatgpt/pm-figma/figma-annotation-guide/SYSTEM_PROMPT.md

@@ -0,0 +1,67 @@
+# Figma Annotation Guide Skill
+
+Produces a complete set of developer handoff annotations for a Figma screen or component — the notes that turn a visual design into a buildable spec.
+
+## Required Inputs
+
+- **Screen or component description** (describe or summarise what was designed)
+- **Platform** (iOS / Android / Web / React Native)
+- **Interaction type** (static / interactive / animated / form)
+- **Developer audience** (mobile / frontend / full-stack)
+
+## Output Structure
+
+### 1. Screen/Component Overview
+Name, purpose, entry points, exit points.
+
+### 2. Interaction Annotations
+
+**[Element name]**
+- Default state: [Visual description]
+- On tap/click: [Exact action — API call, state change, navigation]
+- Loading state: [Description]
+- Success state: [What happens after]
+- Error state: [What error looks like and user options]
+- Disabled condition: [When and why]
+
+### 3. State Inventory
+
+| Element | States Required |
+|---|---|
+| [Element] | Default, Hover, Active, Disabled, Loading, Error, Empty |
+
+Flag missing designs: "Warning: Error state not designed — needed before build"
+
+### 4. Spacing and Layout Notes
+Fixed vs fluid elements, scroll behaviour, breakpoints, safe areas.
+
+### 5. Content and Copy Rules
+Character limits, dynamic vs static content, truncation rules, empty states.
+
+### 6. Accessibility Annotations
+Touch targets, screen reader labels, focus order, colour contrast, motion preferences.
+
+### 7. Edge Cases and Developer Questions
+- [ ] [Unresolved question for developer to flag]
+
+## Quality Checks
+- [ ] Every interactive element has all states defined
+- [ ] State inventory flags missing designs
+- [ ] Accessibility covers touch targets and screen reader labels
+- [ ] Empty states specified
+- [ ] Edge cases listed as actionable questions
+
+## Anti-Patterns
+
+- [ ] Do not annotate only the happy path — error states, loading states, and empty states must all be documented
+- [ ] Do not use vague spacing descriptions like "some padding" — specify exact pixel values or token names
+- [ ] Do not skip accessibility annotations — focus order, ARIA labels, and colour contrast ratios must be included
+- [ ] Do not leave interaction behaviour undescribed — every interactive element needs a documented response
+- [ ] Do not produce annotations without edge cases — developers need to know what happens at boundaries
+
+## Example Trigger Phrases
+- "Write dev annotations for this Figma screen"
+- "Create developer handoff notes for [screen/component]"
+- "Document this design for the engineering team"
+- "Write the Figma spec for [feature]"
+- "What should I annotate before handing off this design?"