Consolidate the properties panel: Position & taille, no more Taille/Survol/duplicate Disposition

- Merge "Taille dans le conteneur" into "Position & taille": a child
  element (posé dans un conteneur/répéteur/groupe de champs) now shows
  greyed-out X/Y (not applicable, it follows its parent's layout) and
  a single Largeur/Hauteur field per axis with a unit selector (%/px)
  instead of the old fixed-px-only sliders capped at 1000 — which was
  the root cause of a landscape-mode bug where a child couldn't be
  made wider than 1000px even though the actual screen was wider.
  New c_size control type (one style key per axis, not two competing
  sliders — an earlier px+% two-slider attempt let the untouched
  slider silently clobber the other's value on every autosave).
- Merge the two "Disposition" groups (visibility + scale, previously
  split apart in UNIVERSAL_CONTROLS by unrelated groups) into one.
- Remove the "Survol" panel: hovering is conceptually a flow trigger,
  not a static element property — to be reintroduced there. The
  underlying data-hover-text/bindHoverTexts runtime is untouched.

static/style.css

@@ -176,6 +176,10 @@ body.builderBody > main.content{ flex:1 1 auto; min-height:0; overflow:hidden; d
 .posGrid{ display:grid; grid-template-columns:1fr 1fr; gap:8px 12px; margin-bottom:14px; }
 .posGrid label{ font-size:11px; color:var(--text-dim); display:flex; flex-direction:column; gap:4px; }
 .posGrid input{ background:var(--panel2); border:1px solid var(--border); border-radius:6px; color:var(--text); padding:6px 8px; }
+.posGrid input:disabled{ opacity:0.4; cursor:not-allowed; }
+.sizeField{ display:flex; gap:4px; }
+.sizeField input{ flex:1; min-width:0; }
+.sizeField select{ width:auto; flex:0 0 auto; padding:6px 4px; }
 
 .controlRow{ margin-bottom:12px; }
 .controlRow > label{ display:block; font-size:12px; color:var(--text-dim); margin-bottom:4px; }