Add MiniMax H3 video provider

[octo-patch]

Reason: Add MiniMax H3 video generation wiring for the V2 create/query/list/delete flow.

Changes:

• Added a MiniMax H3 video provider with request validation, task creation, polling, listing, and deletion helpers.
• Added a dedicated MiniMax H3 tool entry and registered it in the video tool map.
• Added the provider to the default server config and covered the new content-role and validation paths with tests.

Checks:

• python3 -m py_compile on the touched server Python files.
• Direct Python assertions for MiniMax H3 endpoint, content-role, and validation helpers.
• Imported the shared tool registry and confirmed the new MiniMax H3 tool entry is present.

[octo-patch]

Updated the MiniMax H3 V2 request routing so create and delete use /v2/video_generation while query, list, and polling use /v2/query/video_generation. I added coverage for both regional endpoints and all four operation paths; the focused provider suite passes 14 tests, and Python compilation passes for all six PR-touched files.