feat(greenpt): add DeepSeek V4.1 Flash

[robertkeus]

GreenPT now exposes deepseek-v4.1-flash, but its models.dev catalog does not list it. Add the provider entry so clients can discover it, following the GreenPT additions in #6618.

Inherit shared metadata from deepseek/deepseek-v4.1-flash, including text/image input, tool calling, 1M context and 384,000 maximum output tokens. Set GreenPT's documented reasoning_effort values: none, minimal, low, medium, high.

Convert GreenPT's EUR customer prices to USD per million tokens at the ECB's 2026-09-10 rate of 1.1616 USD/EUR:

Token class	EUR/MTok	USD/MTok
Input	0.22	0.255552
Cached input	0.011	0.0127776
Output	1.10	1.27776

Cache writes are not charged; omit that field, matching existing GreenPT entries. The existing deepseek-v4-flash-0731 remains a separate model with its own prices.

Validation: npm run --silent validate passes. npm test in packages/sdk passes generation, typechecking and all 23 tests. Resolved-data assertions verify prices, reasoning controls, modalities and inherited limits. GreenPT grows from 39 to 40 models; every existing resolved catalog entry remains identical. Production inference and the inherited maximum output limit were not tested.

Sources:

• GreenPT model ID, prices and reasoning controls: https://docs.greenpt.ai/deepseek-v4-1-flash
• GreenPT multimodal capabilities: https://docs.greenpt.ai/model-cards
• GreenPT reasoning API: https://docs.greenpt.ai/reasoning
• Cache billing: https://docs.greenpt.ai/prompt-caching
• Shared model limits: https://api-docs.deepseek.com/quick_start/pricing/
• EUR/USD conversion: https://www.ecb.europa.eu/stats/policy_and_exchange_rates/euro_reference_exchange_rates/html/eurofxref-graph-usd.en.html

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