Add API/export contract enforcement checks

[ProfRandom92]

Goal

Add lightweight contract enforcement checks for real Comptextv7 API/export payload shapes using the machine-readable contracts introduced in PR #22.

Background

Comptextv7 now has:

• machine-readable contract schemas under contracts/
• synthetic examples under contracts/examples/
• scripts/validate_contracts.py
• agent CI guardrails

The next step is to validate generated API/export sample payloads against these contracts without requiring a live server or real Daimler data.

Scope

Create a CI-friendly enforcement layer:

• scripts/generate_contract_fixtures.py
• scripts/validate_api_exports.py
• contracts/examples/api-dashboard.example.json
• update .github/workflows/agent-checks.yml
• update docs/API_SURFACE.md
• update docs/AGENT_WORKFLOW.md

Requirements

• Prefer Python standard library only.
• Do not require a live server.
• Do not require real Daimler data.
• Use synthetic fixtures only.
• Do not commit secrets, tokens, cookies, customer data, raw production logs, or proprietary documents.
• Reuse the existing contract validation approach where possible.
• Keep the PR small and reviewable.

Desired behavior

• Generate deterministic synthetic API/export fixtures.
• Validate generated fixtures against contracts/api-dashboard.schema.json.
• Produce docs/reports/api-export-validation-report.md.
• CI should run this check.
• Missing optional runtime components should report a safe skip, not fail.

Acceptance criteria

• API/export fixture generation exists and is deterministic.
• API/export validation exists and runs in CI.
• No live server is required.
• No real Daimler data is included.
• Reports are generated under docs/reports/.
• Future agents can use this as a compatibility gate before dashboard/API PRs.