unify template authoring rules, media workflows, and streaming feedback

[jhe009809-hue]

Summary

This change unifies content-led authoring rules across Design, PPT, and Video workflows.

• Adds shared English authoring and media guidelines with type-specific rules.
• Adds reusable layout catalogs and contracts for slides, sites, and videos.
• Preserves template visual systems while allowing suitable catalog layouts or new layouts when needed.
• Adds media planning and completion checks based on provider capability, authorization, model selection, asset references, and generation receipts.
• Supports multiple media providers, including OpenAI image models and Volcengine Seedream.
• Improves streaming feedback by showing active tool work as lightweight live activity and delaying generated media result cards until the final response is complete.
• Updates bundled templates, plugin manifests, and client/server integration tests.

Validation

• App typecheck passed.
• Server typecheck passed.
• App targeted tests: 127 passed.
• Server targeted tests: 179 passed, 1 skipped.
• Maintainability audit passed with no errors.
• Synced with the latest origin-ssh/main without conflicts.
• Pushed to origin-ssh/Carrie.

Live provider billing, generation quality, and export fidelity still depend on the connected provider and require end-to-end validation.