feat(python-sdk): add VideoOutput type and video support to MultimodalResponse (#469)

[santoshkumarradha]

Summary

• Adds VideoOutput Pydantic model with save(), get_bytes(), and metadata fields (duration, resolution, aspect_ratio, has_audio, cost_usd)
• Adds videos property, has_video property to MultimodalResponse
• Updates is_multimodal, __repr__, save_all to include videos
• Updates FalProvider.generate_video() to return both files (backward compat) and videos

DX

result = await app.ai_generate_video("A cat playing", model="fal-ai/minimax-video/image-to-video")
print(result.has_video)            # True
print(result.videos[0].duration)   # 8.0
await result.videos[0].save("cat.mp4")
print(result.has_file)             # Also True (backward compat)

Test plan

• 5 TestVideoOutput tests (create, metadata, base64, save, error)
• 5 TestMultimodalResponseVideo tests (has_video, is_multimodal, repr, backward compat)
• Full test suite passes, ruff clean

Closes #469

[github-actions]

Performance

SDK	Memory	Δ	Latency	Δ	Tests	Status
Python	7.9 KB	-13%	0.56 µs	+60%	✓	✗

✓ No regressions detected

[github-actions]

📊 Coverage gate

Thresholds from .coverage-gate.toml: per-surface ≥ 86%, aggregate ≥ 88%, max per-surface regression ≤ 1.0 pp, max aggregate regression ≤ 0.50 pp.

Surface	Current	Baseline	Δ
control-plane	87.30%	87.30%	→ +0.00 pp	🟡
sdk-go	90.70%	90.70%	→ +0.00 pp	🟢
sdk-python	93.63%	93.63%	↑ +0.00 pp	🟢
sdk-typescript	92.56%	92.56%	→ +0.00 pp	🟢
web-ui	90.02%	90.01%	↑ +0.01 pp	🟢
aggregate	89.02%	89.01%	↑ +0.01 pp	🟡

✅ Gate passed

No surface regressed past the allowed threshold and the aggregate stayed above the floor.

[github-actions]

📐 Patch coverage gate

Threshold: 80% on lines this PR touches vs origin/main (from .coverage-gate.toml:thresholds.min_patch).

Surface	Touched lines	Patch coverage	Status
control-plane	0	—	➖ no changes
sdk-go	0	—	➖ no changes
sdk-python	0	—	➖ no changes
sdk-typescript	0	—	➖ no changes
web-ui	0	—	➖ no changes

✅ Patch gate passed

Every surface whose lines were touched by this PR has patch coverage at or above the threshold.