[feat] Integrate Kling as optional video generation provider #142

Goal

Add Kling as an optional video-generation provider in OpenDirector, alongside existing media providers (e.g. MiniMax H3).

Scope

• Confirm official endpoint, auth, model ids, async job semantics, and result download from vendor docs; cite them in implementation notes.
• Use the existing model-connection / provider configuration path; optional only; do not change the default provider.
• Support text-to-video and, if documented, image/first-frame to video; wire jobs and results into existing generation, canvas, and asset flows.
• Map duration, resolution, and reference options only when the official API supports them and they fit current capability contracts.
• Handle auth failures, content policy / moderation codes, rate limits, timeouts, and server errors with clear messages (do not map them to a vague generic failure); never log API keys.
• Document setup, capabilities, and limits.

Acceptance (implementer / reviewer owns evidence)

• With valid credentials, users can submit a Kling job from OpenDirector, track status, and adopt the result into the project.
• Failures are explicit and isolated from other providers.
• Evidence includes model id, API version, and screenshot or recording.

Notes

Product requirement only. Implementation and acceptance evidence are left to the assignee / community.