fix(words): "+" inserter only shows in the rail gap between blocks

Previously the "+" snapped to any seam within 18 px of the cursor's
Y — which meant it appeared even when the cursor was hovering on a
block's body (near its top/bottom edge) or in the rail aligned with
the block. That clashed with the grip's territory.

Per user spec: when the cursor is on a block (text or rail-aligned),
the grip is the actor — the "+" should be hidden. The "+" only
surfaces when the cursor is in the rail column AND vertically
positioned in a gap BETWEEN two blocks.

Two new gates added to `findSeamForCursor`:
1. **Out-of-content X**: if `e.clientX` falls inside the content
   box's horizontal extent (the editor's text area), return null
   immediately. The cursor is reading text or near the toolbar/
   status row, not the rail.
2. **Out-of-block Y**: if `e.clientY` falls inside ANY top-level
   block's vertical band, return null. The block-handle owns that
   slot.

Only when both gates pass do we snap to the nearest seam. The
existing `dragover` path is untouched — drag indicator still works
inside the content area because the drag operation has different
ergonomics (you're actively moving a block, the line is the drop
target, not a discoverability cue).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/uix/eidos/components/words/words-block-inserter.svelte

@@ -73,13 +73,39 @@
 		return seams;
 	}
 
+	/**
+	 * The "+" only shows up when the cursor is OUTSIDE the content box
+	 * (i.e. in the rail column) AND vertically positioned in a gap
+	 * between two blocks. Hovering over a block — either on its text
+	 * or on the rail aligned with the block — surfaces the grip
+	 * instead (block-handle is the actor there). Per user spec:
+	 * "el + solo aparece en la banda entre bloques".
+	 */
 	function findSeamForCursor(e: MouseEvent, content: HTMLElement): Seam | null {
+		const contentRect = content.getBoundingClientRect();
+		// Cursor inside the content's horizontal extent → user is reading
+		// text or is in the editor body, not the rail. No "+".
+		if (e.clientX >= contentRect.left && e.clientX <= contentRect.right) {
+			return null;
+		}
+		// Cursor inside ANY block's vertical band → grip's territory.
+		const blocks = Array.from(
+			content.querySelectorAll<HTMLElement>(
+				'[data-words-node="block"][data-words-path]'
+			)
+		).filter((b) => !(b.getAttribute('data-words-path') ?? '').includes('.'));
+		for (const block of blocks) {
+			const r = block.getBoundingClientRect();
+			if (e.clientY >= r.top && e.clientY <= r.bottom) return null;
+		}
+		// Cursor is in the rail AND between blocks — snap to the nearest
+		// seam. No X-bound check needed; we already know X is in the rail.
 		const seams = listBlockBoundaries(content);
 		let best: Seam | null = null;
 		let bestDelta = SEAM_RANGE_PX;
 		for (const s of seams) {
 			const delta = Math.abs(s.y - e.clientY);
-			if (delta < bestDelta && e.clientX >= s.left - 32 && e.clientX <= s.right + 32) {
+			if (delta < bestDelta) {
 				best = s;
 				bestDelta = delta;
 			}