kb: retire pi-installation association (OMP is the primary harness)

Purge live-state claims that ~/.pi is our harness; keep general
pi documentation in omp-docs/ and dated historical records.

- README.md: single config source; Legacy Notes reworded
- AGENTS.md: drop 'like ~/.pi did' framing
- APPEND_SYSTEM.md: okf-spec -> omp-docs/references/okf-spec.md
- dotfiles/zsh/.zshrc: systemprompt alias -> APPEND_SYSTEM.md
- managed skill llm-fleet-model-swap + model_config_sync skill:
  single-source models.yml; validation script YAML-only
- memories (MEMORY.md, memory_summary.md, learned.md): single source
- omp-docs: .okf root -> ~/.omp/omp-docs; de-live pi-era claims in
  pi/index.md, pi-web-access.md, engineering/agents-files.md

omp-docs/.okf/config.yaml

@@ -7,7 +7,7 @@ bundle:
   version: "0.1"
   author: "pi agent system"
   description: "Cached documentation for tools, configurations, and systems used during pi agent sessions."
-  root: "/home/dank/.pi/agent/docs"
+  root: "~/.omp/omp-docs"
 
 generator:
   # Index generation settings