Threat detail / response view inside the unified shell

[CodeBuildder]

Context

Clicking a threat in the shell opens a detail panel with diagnosis, fragility context, and response options. Parent: #87.

Acceptance Criteria

• Threat detail panel shows: severity, attack_stage, diagnosis, targeted entity fragility_score
• Panel links to correlated Phoenix reliability events on the same entity (if any exist)
• Response actions (quarantine, enforce policy) are triggerable from the panel
• Panel reads all data from world model APIs — no direct Argus internal API calls from the shell

Dependencies

Blocked by: none | Blocks: none

Notes

No model tier. UI work.