docs(shared): framework-neutral concept note + shared-core contract

First artifact in the framework-neutral shared core (R1 effectuated). CONCEPT.md
is a plain-language business description of the method for a non-specialist
audience; README.md documents the shared-core contract (consumed unchanged by
both the MAF impl and the future Claude Agents SDK sibling; extract to commons
repo via git subtree split when sibling work starts). English per the repo's
documentation-language convention + open-publish intent.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019any9zfGNNwWJPX5Zq2QRz

shared/README.md

@@ -0,0 +1,31 @@
+# shared/ — framework-neutral core
+
+This directory holds the parts of the project that are **independent of any AI agent
+framework** and are meant to be **shared, unchanged, between both reference
+implementations**:
+
+- **this repository** — the method built on Microsoft Agent Framework (MAF);
+- **a sibling repository** (built later, in sequence) — the same method on the
+  **Claude Agents SDK**.
+
+Sharing one identical core is what makes the two implementations a *fair comparison*:
+both consume the same concept, the same example data, and the same expected outcomes,
+so the only thing that differs is the agent framework itself.
+
+## Contents (growing)
+
+- [`CONCEPT.md`](CONCEPT.md) — the business concept, written for a non-specialist
+  (e.g. a business developer at another company).
+- *(planned)* the method specification, the example knowledge bundles (OKF / LLM-wiki),
+  the expert-reviewer persona, and the golden-suite of expected validator outcomes.
+
+## Rules
+
+- **Nothing in here may import or depend on a specific agent framework.** If it does,
+  it does not belong in `shared/`.
+- **Repo layout (decision R1, 2026-06-26):** the shared core lives here for now. When
+  work on the sibling repository begins, it will be extracted into its own repository
+  (e.g. `portfolio-optimiser-commons`) via `git subtree split`, and both implementation
+  repos will consume it. This defers cross-repo plumbing until it is actually needed.
+
+See the target picture for the full architecture: `docs/plan/2026-06-26-maalbilde-agentic-loop.md`.