feat(ingress): add fail-fast readiness and direct fpga ingress mode

[Lythaeon]

Summary

• add explicit ingress readiness validation before runtime bootstrap work and fail fast per active mode
• add direct FPGA ingress mode (auto|mock_dma|direct_device|external_socket) with direct device path support
• expand FPGA adapter to support direct device and external socket ingestion with strict readiness checks
• keep kernel bypass readiness strict (including OpenOnload readiness and external socket checks)
• update runtime config model, sample config, and operator docs for professional deployment

Risk Notes / Regressions Considered

• startup is now stricter and will exit earlier for missing ingress prerequisites
• FPGA vendor/mode mismatches are rejected explicitly instead of silently falling back
• direct-device ingestion assumes line-framed payload output from vendor bridge/driver stream; malformed frames are dropped and logged

Validation Performed

• cargo make format-check
• cargo make test (81 tests passed)
• cargo make clippy
• cargo test -q (79 unit/integration + 2 e2e passed)