feat(office): add Atlas Cloud video provider

[binyangzhu000-sudo]

Summary

• add Atlas Cloud as an optional Seedance provider while keeping Ark as the default
• support text-to-video plus first/last-frame image-to-video with provider-specific model aliases
• issue generation POSTs once and bound GET polling, including transient GET retry handling
• document Atlas configuration and keep plugin versions synchronized

Validation

• python3 -m pytest office/tests/test_generate_video_atlas.py -q (4 passed)
• python3 plugin-optimizer/scripts/validate-plugin.py office (passed; 3 existing advisory warnings)
• uv run office/skills/generate-video/scripts/generate_video.py --help
• live Atlas smoke: one accepted POST, bounded GET polling, completed with one HTTPS output
• git diff --check

Existing test failure

The full Office suite has one unrelated failure in xml_text_overlap_lint_test.py due a comma/full-width-comma expectation mismatch. The same focused test fails on unmodified origin/develop.

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