#289 CONV-328: Add API examples and curl snippets

Summary

• Adds 6 executable curl examples covering the full happy path
• Examples use /api/v1, Authorization: Bearer, and no real secrets
• Covers: upload, list targets, estimate, create, poll, download

Test plan

• Test written first — fails before examples added
• composer test passes (617 tests)

🤖 Generated with Claude Code

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Summary by cubic

Fulfills CONV-328 by adding six runnable curl examples to the API docs that show the end-to-end v1 conversion flow: upload, list targets, estimate, create, poll, and download. Uses /api/v1 and Authorization: Bearer, and adds a feature test to ensure the snippets render on /docs/api.