Center tagline bands, frame anchors evenly, fill to the window edge, and resize columns from their grip

Every tag band (workspace, column, pane) is centred in its row, so text sits
at one baseline offset. Anchors are inset from the column rule by that same
margin, so they are square and the band frames them on the left, top and bottom;
the pane mark moves to stay centred. When the window is not a whole number of
cells, the bands, rules, spines and scroll thumbs at the right and bottom edges
run on through the leftover pixels.

A column grip dropped short of another column's place now moves the column's
left edge, with a dashed rail preview, sharing setColumnPairWidth with the
border drag. A release still on the grip changes nothing, and a pair too
narrow for two MINW columns is left alone.

PARDES_TEST_PAD adds leftover pixels to a test-mode window and capture.

1 files changed, 2 insertions, 3 deletions

diff --git a/src/macos/Sources/PardesView.swift b/src/macos/Sources/PardesView.swift
index 5ad09c38..70f467e3 100644
--- a/src/macos/Sources/PardesView.swift
+++ b/src/macos/Sources/PardesView.swift
@@ -523,9 +523,8 @@ private struct TaglineMetrics {
 
     /// Where this band sits inside row `row`, measured down from the row's top.
     /// The rule belongs to the core (`pardes_tagline_band_offset`) so that this
-    /// shell and the SDL one cannot disagree about it: row zero and the first
-    /// pane-tag row meet at a shared rule, a Tagbottom band on the last row
-    /// faces the window edge, and everything between is centred.
+    /// shell and the SDL one cannot disagree about it: every band is centred,
+    /// except a Tagbottom band on the last row, which faces the window edge.
     func top(row: Int, canvasHeight: CGFloat) -> CGFloat {
         CGFloat(pardes_tagline_band_offset(
             UInt16(clamping: row), Float(canvasHeight * scale), cellPixels, bandPixels)) / scale