docs: add Signal & Noise interactive artifact

Archive a self-contained HTML copy of the design rationale artifact —
the interactive Signal & Noise analysis of Karpathy's pattern that
produced memex. Fully self-contained (inline CSS + JS, only external
dependency is Google Fonts), works offline, renders identically in any
modern browser.

Updated the README Credits section to link:
1. Live interactive version at eric-turner.com/memex/signal-and-noise.html
2. Original Claude artifact
3. Archived copy in this repo
4. Condensed written version in DESIGN-RATIONALE.md

The archived HTML means the analysis survives even if the live site or
the Claude artifact URL ever goes away.

README.md

@@ -413,14 +413,21 @@ and how to adapt for other agents).
 
 **Design process** — this repo was designed interactively with Claude
 as a structured Signal & Noise analysis before any code was written.
-The interactive design artifact is here:
-[The LLM Wiki — Karpathy's Pattern — Signal & Noise](https://claude.ai/public/artifacts/0f6e1d9b-3b8c-43df-99d7-3a4328a1620c).
-That artifact walks through the seven real strengths and seven real
+The analysis walks through the seven real strengths and seven real
 weaknesses of the core pattern, then works through concrete mitigations
 for each weakness. Every component in this repo maps back to a specific
 mitigation identified there.
-[`docs/DESIGN-RATIONALE.md`](docs/DESIGN-RATIONALE.md) is the condensed
-version of that analysis as it applies to this implementation.
+
+- **Live interactive version**:
+  [eric-turner.com/memex/signal-and-noise.html](https://eric-turner.com/memex/signal-and-noise.html)
+  (click tabs to explore pros/cons, vs RAG, use-case fits, signal
+  breakdown, and mitigations)
+- **Original Claude artifact**:
+  [The LLM Wiki — Karpathy's Pattern — Signal & Noise](https://claude.ai/public/artifacts/0f6e1d9b-3b8c-43df-99d7-3a4328a1620c)
+- **Archived copy in this repo**:
+  [`docs/artifacts/signal-and-noise.html`](docs/artifacts/signal-and-noise.html)
+- **Condensed written version**:
+  [`docs/DESIGN-RATIONALE.md`](docs/DESIGN-RATIONALE.md)
 
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