feat: add MCP Apps extension substrate #765

Job	Run time
Rust clippy	0s
Rust test (Redis-backed paths)	0s
Supply-chain vet	0s
Documentation	0s
Resolve Rust Python release matrix	0s
Rust fmt	0s
Rust build (${{ matrix.os }})	0s
License check (workspace)	0s
Dependency policy	0s
Build wheels (${{ matrix.os }})	0s
Rust test (${{ matrix.os }})	0s
Benchmarks (build check only)	0s
Release wheels (${{ matrix.platform }})	0s
Release sdist	-1s
Publish Rust Python packages	-1s
Coverage	-6s
	-8s

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