System detailed design: four-model cross-review complete

Add system-detailed-design.md (2033 lines, 23 sections) derived from
frozen baselines and overview. Complete four-model cross-review:
- DeepSeek: baseline coverage audit (PASS, 9.6/10)
- MIMO 2.5 Pro: internal consistency (PASS, 9.4/10)
- GPT-5.5 Pro: baseline conflict detection (Requires repair)
- Opus 4.8: validation + root cause analysis (CONDITIONAL PASS, 9.1/10)

Key findings requiring resolution before freeze:
- P1-01: Worker exit code semantic conflict (baselineV1 vs overview)
- P1-02: PromptLayerLevel enum vs L0-L9 layer name mismatch
- P1-03: EventStore.project() error handling undefined
- P1-04: PromptLayerLoader interface incomplete for 10 layers

Coverage verified: 100% contracts, events, DB schema, state machines.
Architecture validated: no circular dependencies, proper separation.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

AirPlan/plan.md

@@ -33,6 +33,7 @@ Implementation must follow these canonical V1 documents:
 | Requirements | `AirPlan/docs/analysis/requirements.md` |
 | Solution architecture | `AirPlan/docs/architecture/solution-architecture.md` |
 | System overview design | `AirPlan/docs/architecture/system-overview-design.md` |
+| System detailed design | `AirPlan/docs/architecture/system-detailed-design.md` |
 | C4/module view | `AirPlan/docs/architecture/c4/module.md` |
 | Baseline | `AirPlan/docs/architecture/baselineV1.md` |
 | DB schema | `AirPlan/docs/architecture/db-schema-v1.md` |