ECDT: add deterministic scenario engine

[aeonmatrixcommand-debug]

Adds a deterministic, side-effect-free Scenario Engine to the Enterprise Cognitive Digital Twin.

Changes:

• Add ECDTScenarioEngine
• Add immutable ScenarioEvaluation result model
• Rank scenarios by impact, confidence, and risk
• Add governance policy blocking
• Add deterministic audit trace
• Export Scenario Engine through the ECDT package

Safety / Governance:

• No execute/apply/deploy/promote interface
• No production side effects
• execution_authorized remains false
• Policy-blocked scenarios cannot be recommended

Validation:

• Scenario Engine tests: 8 passed
• ECDT tests: 26 passed
• Full suite: 277 passed, 1 skipped
• git diff --check: passed

Scope:

• src/intelligence/ecdt/init.py
• src/intelligence/ecdt/scenario_engine.py
• tests/ecdt/test_scenario_engine.py