fix(forma): full-bleed cover at `full` so its corners match the card

The previous fix dropped the cover to a clean --radius-xl, but a sharp
16px corner floating inside the card's 169px pill curve still read as
broken. The only way a child's corner can match a `full` parent (whose
radius caps per-dimension, so concentric math is impossible) is to let
the parent CLIP it: at `full` the cover now bleeds edge-to-edge with no
radius of its own, and the card's overflow:hidden + real corner round
its top to match exactly. Updated SHAPE_ENGINE_RFC §5 accordingly.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/uix/eidos/SHAPE_ENGINE_RFC.md

@@ -105,9 +105,11 @@ nada → cero rotura):
 > se **recorta a la mitad de la dimensión menor de cada elemento** — un contenedor alto y su hijo
 > ancho (p. ej. 16:10) recortan a valores distintos, así que **no pueden ser concéntricos**. `full`
 > es para **hojas** (chips · botones · avatares · inputs-píldora), no para contenedores con hijos
-> que deban encajar. La regla `[data-shape-nest]` se desactiva ahí; el hijo se queda en un radio
-> finito limpio. El demo `/temas/forma` lo refleja: al elegir `full`, el toggle "radios
-> concéntricos" se inhabilita («n/a a full — geometría de hoja») y la carátula cae a `--radius-xl`.
+> que deban encajar. La regla `[data-shape-nest]` se desactiva ahí. El demo `/temas/forma` lo
+> refleja: al elegir `full`, el toggle "radios concéntricos" se inhabilita («n/a a full — geometría
+> de hoja») y la carátula **sangra a borde completo sin radio propio** — el `overflow: hidden` + la
+> curva real del card la recortan para que su esquina superior coincida exacta con la del card (la
+> única forma de "encajar" sin radios finitos: dejar que el padre recorte al hijo, no calcular).
 
 ## 6. Fases (la flexibilidad va horneada en cada una)
 

web/routes/temas/forma/+page.svelte

@@ -349,10 +349,11 @@
 		overflow: hidden;
 	}
 	.cover-naive { border-radius: var(--radius-xl); }
-	/* at `full` the card is a pill (radius caps to half its width); a 16:10 cover would cap to half
-	   its HEIGHT → a horizontal pill that can't be concentric with a vertical-pill parent. Concentric
-	   needs finite radii. So at full the cover stays cleanly rounded (a leaf), never "pill-in-pill". */
-	.cover-full { border-radius: var(--radius-xl); }
+	/* at `full` the card is a pill (radius caps to half its shorter side); a finite-radius cover
+	   floating inside reads as broken, and a concentric cover is impossible (different aspect ratios
+	   cap differently). So at full the cover bleeds edge-to-edge with NO radius of its own — the
+	   card's overflow:hidden + its real corner clip the cover's top to match the card exactly. */
+	.cover-full { margin: 0; border-radius: 0; }
 	.player-play {
 		inline-size: 3.25rem;
 		aspect-ratio: 1;