v5.x — Sonic-3 Architecture Stabilization & GCS Integration

NDF v5.x — Sonic-3 Architecture Stabilization & GCS Integration

This release finalizes the structural upgrade of the Hybrid Audio API:

• Full structured-path GCS integration (stems/name|developer|script)
• Cache router refactor with proper GCS delegation + diagnostics
• New scripts_engine module (extensible script rotation core)
• Updated rotation engine (script-aware, dataset-safe)
• Hardened CLI (v5.2+) with secure headers, timeout handling, and route alignment
• Makefile v5.3 (batch pipeline, validation routines, cache tooling)
• Updated end-to-end tests: rotation + cache + GCS pathing
• New test suite for scripts, stem-path resolution, bucket checks
• Internal contract documentation expanded (payload, naming, timing)
• Endpoint Reference v5.x reformatted and aligned with routers
• Stability, observability, and NDF guarantees preserved throughout

This commit represents the completion of today's multi-phase upgrade:
Phase 1 (GCS core), Phase 2 (structured stems), Phase 3 (script engine),
Phase 4 (test rebuild), Phase 5 (CLI/Makefile integration).

Hybrid Audio API is now ready for production alignment and UI integration.