docs: accessible figure legends (README.md) for all figures

One self-contained README.md per results/ figure folder (Layer 1 E1-E6
and Layer 1.5 bridge/collapse/grounding/architectures/recombination):
plain-language claim, setup, a compact symbol glossary, a panel-by-panel
walkthrough, and the takeaway + falsifier. Auto-renders when browsing the
folder; carries the honest caveats (grounding's ruler reframing, the
excluded VAE).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

results/E2/README.md

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+# E2 — A tiny dose of real data rescues diversity (the headline)
+
+**Claim tested:** how much *real* data must you mix back in each generation to stop collapse — a
+lot, or a little?
+
+**Setup (Layer 1, pure math).** `K = 1000` items, Zipf truth `p*`, `n = 200` inherited samples per
+generation, 500 generations, 100 repeats. Each generation we also mix in `m` fresh **real** samples
+drawn from `p*`. The knob swept is the **grounding fraction** `g = m/(n+m)` — the share of the
+training pool that is real — across `g ∈ {0, 0.005, 0.01, 0.02, 0.05, 0.1, 0.2, 0.4}`.
+
+### Symbols
+- **`g`** grounding fraction (share of real data); **`g*`** the *critical* value that restores diversity.
+- **`p*`** truth, **`p_t`** model, **`H`** diversity, **`H*`** truth's diversity.
+- **grounding = "immigration"** in the genetics analogy: real samples are migrants that re-introduce alleles drift keeps killing.
+
+### The four panels
+1. **Trajectories.** Diversity `H` over generations, one line per `g` (dark = dry, bright = more
+   grounding). `g = 0` slides toward 0; any `g > 0` levels off on a plateau — the collapse is
+   arrested.
+2. **The phase boundary (the headline).** Dots = stationary diversity vs `g`; the black dashed curve
+   is the *exact* closed-form equilibrium `H_eq`; the red line marks the critical
+   **`g* ≈ 0.048` (95% CI [0.047, 0.050])** where `H` reaches 95% of the truth's diversity. Only
+   **~5% real data** buys back essentially all the diversity. The `g = 0` point is drawn hollow (it
+   is still sliding — its true equilibrium is 0).
+3. **Tail coverage.** Fraction of the rare tail retained, by item-count (red) and truth-mass-weighted
+   (purple). Both rise with `g` but stay modest at feasible grounding: a little grounding restores
+   *diversity* long before it restores the *deep* tail — which motivates E4 (recombination) and E6.
+4. **Per-rarity band.** The tail split into rarity bands (bright = shallowest, dark = deepest). Deep
+   bands lag: an item survives only once `m·p*ᵢ ≳ 1` (enough real samples per generation to land it
+   at least once). The sharp threshold lives here, in discrete item survival — not in the smooth `H`.
+
+### Takeaway
+There is a **critical grounding fraction `g* ≪ 1`**: a small, constant trickle of reality
+indefinitely holds off collapse. **Falsifier (not triggered):** if diversity had only recovered as
+`g → 1`, the practical thesis would die. It recovers at `g ≈ 0.05`.