Implement deferred MCP deck export and full stdio runtime verification

[alonshoa]

Follow-up from #9.

Context

Issue #9 delivered the minimal local stdio MCP server surface over the shared Studio services, including catalog/scene inspection, validation, render, build, log, and artifact access.

The remaining items are intentionally deferred pieces that should not block closing the minimal MCP server phase.

Scope

• Implement a real export_deck service instead of returning unsupported.
• Decide initial supported export format(s), such as HTML, PPTX, or another delivery format.
• Ensure the MCP export_deck tool reuses the same export service that any CLI/export workflow uses.
• Add tests for successful export, invalid deck IDs, unsupported formats, and failed export results.
• Verify the installed manim-mcp stdio server can be constructed and launched in the intended devcontainer/WSL environment with the mcp SDK installed.
• Update MCP documentation with the supported export formats and any runtime prerequisites.

Acceptance criteria

• export_deck returns a successful structured response for at least one supported format.
• Export artifacts are discoverable through build/artifact inspection where applicable.
• Unsupported formats return a stable structured error.
• Local stdio startup is verified in the intended development environment.