feat(mcp): bundle VidXP plugin and install it from Desktop

[tulayha]

Summary

• Bundle VidXP’s ingest and evidence skills with its local MCP server and optional MCP Apps UI.
• Add a Desktop Set up in Codex action that exports a target-specific local marketplace and installs the plugin through Codex, while retaining Copy MCP setup for other clients.
• Keep video data, model execution, and STDIO MCP local; no storage/model migration or index rebuild is required.

Validation

• uv run --no-sync ruff check .
• uv run --no-sync python -m pytest -q — 674 passed, 5 skipped, 95 subtests.
• npm --prefix desktop run check — typecheck, lint, 38 tests, production build.
• cargo test --locked --manifest-path desktop/src-tauri/Cargo.toml — 79 passed.
• npm --prefix desktop run model-catalog:check
• npm --prefix desktop run notices:check
• npm --prefix desktop run sidecar:windows
• Isolated wheel build — plugin bundle and vidxp-codex-plugin entry point included.
• Bundled Codex plugin manifest/structure validation passed.