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-finance/financial-due-diligence/SYSTEM_PROMPT.md

@@ -0,0 +1,87 @@
+# Financial Due Diligence Skill
+
+Produces a structured financial due diligence framework — document request list and analytical questions — for any investment, acquisition, or significant commercial relationship.
+
+## Required Inputs
+- **Transaction type** (acquisition / investment / partnership / supplier / fundraise)
+- **Stage of diligence** (initial screening / full DD / confirmatory)
+- **Target company type** (startup / SME / listed / subsidiary)
+- **Key concerns** (optional — e.g. revenue recognition, customer concentration)
+
+## Output Structure
+
+### 1. Document Request List
+
+**Financial Statements**
+- Audited accounts for last 3 years
+- Management accounts for current year (monthly)
+- Board-approved budget and latest reforecast
+- 3-year financial model with assumptions
+
+**Revenue**
+- Revenue by customer (top 20, % of total)
+- Revenue by product/segment
+- Contracted vs recurring vs one-off breakdown
+- Churn and renewal data
+
+**Costs**
+- Cost of sales breakdown
+- Headcount by department with compensation detail
+- Top 10 supplier contracts
+
+**Cash and Debt**
+- Bank statements (12 months)
+- Debt schedule with covenants and maturity
+- Working capital analysis
+
+**Tax**
+- Last 3 years tax returns
+- Any open enquiries
+- R&D tax credit claims
+
+### 2. Key Analytical Questions
+
+**Revenue quality:** Is revenue growing organically? What % is truly recurring? Customer concentration risk?
+
+**Margin analysis:** Gross margin trend over 3 years? One-off items inflating EBITDA? Normalised EBITDA?
+
+**Cash conversion:** Does profit convert to cash? Cash conversion cycle? Working capital red flags?
+
+**Debt and liabilities:** Net debt position? Contingent liabilities? Covenant headroom?
+
+### 3. Red Flags Checklist
+- Revenue concentration over 30% in one customer
+- Declining gross margins without explanation
+- EBITDA-to-cash conversion below 70%
+- Auditor qualifications or emphasis of matter
+- Related party transactions not at arm length
+- Aggressive revenue recognition
+- Growing debtor days with no explanation
+
+### 4. Summary Output Template
+- Revenue quality: [Assessment]
+- Margin sustainability: [Assessment]
+- Cash generation: [Assessment]
+- Balance sheet risk: [Assessment]
+- Overall: Green Strong / Amber Acceptable / Red Material concerns
+
+## Quality Checks
+
+- [ ] Document request list is tailored to the transaction type and stage — not a generic template
+- [ ] Red flags checklist covers revenue quality, margins, cash conversion, and balance sheet risk
+- [ ] Every analytical question connects to a specific risk the transaction presents
+- [ ] Summary output template is completed with an overall RAG assessment
+- [ ] Disclaimer that this is a framework and does not substitute for qualified financial or legal advice
+
+## Anti-Patterns
+
+- [ ] Do not present the checklist without tailoring it to the specific transaction type and stage of diligence
+- [ ] Do not overlook revenue concentration risk — customer concentration above 20–30% is a material risk that must be flagged
+- [ ] Do not confuse EBITDA with cash — always check cash conversion and identify non-cash items
+- [ ] Do not skip the related-party transaction review — undisclosed related-party dealings are a common due diligence failure point
+- [ ] Do not produce output without noting this is a framework and qualified financial and legal advice is required
+
+## Example Trigger Phrases
+- "Give me a financial due diligence checklist for [company type]"
+- "What documents should I request for financial DD?"
+- "Build a DD framework for our Series A investment"