Add MiniMax v2 text-to-video generation

[octo-patch]

Reason: iPolloWork's Media Center does not support MiniMax v2 text-to-video tasks or task queries.

This change:

• registers the MiniMax-H3 model and global and China v2 endpoints;
• creates prompt-only video tasks with validated duration, resolution, ratio, and callback fields;
• queries regional tasks and normalizes both create and query task identifiers;
• keeps the API key server-side and adds focused request, parsing, and validation coverage.

Checks:

• bun test ./apps/server/src/extensions/media-center.test.ts
• pnpm --filter ipollowork-server typecheck
• node .codex/skills/ipollowork-maintainable-code/scripts/audit-changes.mjs
• git diff --check

No runtime recording was captured because this is a server-side integration and no live provider credentials were used; the focused tests exercise the outbound payloads and task responses.