[MAJOR] §3: keystone_agents library still built despite ADR-015 extraction

[mvillmow]

Finding

Severity: MAJOR
Section: 3
Evidence: CMakeLists.txt:316-331
Principle: MODULARITY

The keystone_agents library (ChiefArchitectAgent, ComponentLeadAgent, ModuleLeadAgent, TaskAgent) is defined, compiled, and shipped as a deliverable of this repository. Per ADR-015, these belong in ProjectAgamemnon. The CMakeLists.txt build configuration has not been updated to reflect the accepted architecture decision.

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Part of #504