feat: add phoenix-self example — Phoenix specs itself (dog-food)
Decompose PRD into 6 focused specs: ingestion, canonicalization,
implementation, integrity, operations, platform. Each has full
implementation stubs with Phoenix metadata, server, and tests.
Pipeline eval on its own PRD: recall 97%, typeAcc 86%, coverage 100%,
D-rate 8%, hierarchy 99%. Composite score 0.9445 across 18 total specs.
All 52 example tests + 413 root tests pass.