One Layer for tags, notices, headers and bodies; a taller tag is one layer of rows; wire v8

src/Layer.zig merges TagLayer and BodyLayer. `rows` (0 = no layer) and a
cursor at {x, y}. A tag of N rows is ONE layer of N grid rows: tagHit answers
the row as `line`, bodyHit keeps its meaning, and the per-line layer bases
(TAG_LINE_LAYER_BASE, HEADER_LINE_LAYER_BASE) are gone, not aliased.

Wire v8, the one bump: tag layers carry rows and cursor y, and the frame
carries the placed region list. v7 and v9 peers are refused in both
directions (server test over both, a new frontend test over both).

web: tag_layer_value 11 = rows, 12 = cursor y; app.mjs lays every row.
macOS: the Zig side compiles against Layer; pardes.h still sees one row
per tag layer (accepted, the macOS shell is ignored for now).

No visual change: snapshot goldens and the 17 GUI goldens byte-identical.

Shared files touched: pardes.zig, Messages.zig, gui.zig, macos.zig,
detached/client.zig, detached/server.zig, detached/wire.zig (plus web.zig,
app.mjs, edit.zig, look.zig). Not touched: mouse.zig, tagline.zig,
colors.zig, tty.zig, dump.zig, exec.zig, host_io.zig, panes.zig.

1 files changed, 3 insertions, 3 deletions

diff --git a/src/Messages.zig b/src/Messages.zig
index 7334de95..b7153e5c 100644
--- a/src/Messages.zig
+++ b/src/Messages.zig
@@ -747,7 +747,7 @@ test "a builtin announces itself on the message row, and Verbose silences it" {
     _ = try p.render(frame.allocator());
     const r = p.rects[p.active];
     const band = for (p.surface.tagLayers()) |*layer| {
-        if (layer.cols != 0 and layer.kind == .notice) break layer;
+        if (layer.rows != 0 and layer.kind == .notice) break layer;
     } else return error.NoNoticeBand;
     try std.testing.expectEqual(@as(u16, 1), band.viewport.h);
     try std.testing.expectEqual(if (p.settings.tag_bottom) r.y else r.y + BOX_H, band.viewport.y);
@@ -794,7 +794,7 @@ test "notices stack over the body's top rows without moving them" {
 
     var seen: usize = 0;
     for (p.surface.tagLayers()) |*layer| {
-        if (layer.cols == 0 or layer.kind != .notice) continue;
+        if (layer.rows == 0 or layer.kind != .notice) continue;
         try std.testing.expectEqual(@as(u16, 1), layer.viewport.h);
         // Sized to its own message, right up against the pane's right edge --
         // not the width of the pane.
@@ -814,7 +814,7 @@ test "notices stack over the body's top rows without moving them" {
     _ = frame.reset(.retain_capacity);
     _ = try p.render(frame.allocator());
     for (p.surface.tagLayers()) |*layer|
-        try std.testing.expect(layer.cols == 0 or layer.kind != .notice);
+        try std.testing.expect(layer.rows == 0 or layer.kind != .notice);
 }
 
 test "an idle core wants no wake and a lingering message sleeps to its linger's end" {