fix(icons): stop macOS drawing the app icon on a legacy plate (#40)

On macOS 26+ the Dock and any launcher that resolves app icons through
NSWorkspace.icon(forFile:) (Spotlight, Vicinae, Raycast, ...) drew a grey
rounded-square "legacy plate" behind Gridline's icon, i.e. a white border
around the app icon at every render size below ~72px.

Reproduced outside any launcher: NSWorkspace.icon(forFile:) on
Gridline.app returns the plated icon at 16-64px and the clean icon at
>=72px. The trigger lives in icon.icns, not in the app -- moving that file
into Zed.app reproduces the border, moving Zed's icns into Gridline.app
removes it.

Two things in the file cause it:

  - ic12 (64x64)                     -> plates the 40-64px range
  - is32/s8mk (16x16 RGB+mask)
    il32/l8mk (32x32 RGB+mask)       -> plates the 16-32px range

macOS treats padded small representations as legacy, and this icns carries
them in both places.

Fix, in two parts.

1. Strip those chunks. scripts/fix-icns.mjs does it; `tauri icon` re-emits
   them on every run, so it has to be a committed, repeatable step.
   scripts/verify-app-icon.mjs is the regression check: it builds a
   throwaway .app around the committed icon.icns, asks AppKit to render it
   at 16..512px and fails if any size comes back plated. It fails (6/11
   plated) on the previous icns and passes on this one.

2. Regenerate the raster set from icon.svg via
   scripts/regenerate-icons.sh, so the icons directory matches its source
   of truth again. The SVG has been full-bleed since the initial commit
   (md5 unchanged at d872e42/3dab09f/6854d88/HEAD) while the rasters were
   replaced with a hand-tuned padded version at v0.2.0 and had drifted
   from it ever since. The script generates into a temp dir because
   `tauri icon` only takes one output directory and would otherwise drop
   generated android/ and ios/ trees into the desktop-only icons dir.

No visual change on macOS: IconServices normalizes app-icon artwork when
rendering, so padded and full-bleed sets come out pixel-identical there
(same bbox and art fraction at 48/128/512px).

Windows and Linux do consume the PNG/ICO directly, so the icon there does
change from padded to full-bleed -- consistent with the SVG, but a
visible difference worth eyeballing before release.

Verified: verify-app-icon passes at 16, 24, 32, 40, 48, 64, 72, 96, 128,
256, 512px; iconutil and `file` still decode the new .icns and .ico
(6 sizes); frontend tests pass (131 files / 1134 tests).

scripts/fix-icns.mjs

@@ -0,0 +1,143 @@
+#!/usr/bin/env bun
+/**
+ * Strip the icon representations that make macOS render Gridline's icon on a
+ * "legacy plate" at small sizes.
+ *
+ * ## Why this exists
+ *
+ * On macOS 26+ (Tahoe) IconServices wraps *legacy* app icons in a light
+ * rounded-square plate for render sizes below ~72px. `tauri icon` emits exactly
+ * those legacy representations, so the artifact shows up in the Dock and in any
+ * launcher that resolves app icons through `NSWorkspace.icon(forFile:)`
+ * (Spotlight, Vicinae, Raycast, …): the app icon gets a white/grey border.
+ *
+ * Two representations in `tauri icon` output trigger it, independently:
+ *
+ *   - `ic12`  (64x64)               -> plates the 40-64px range
+ *   - `is32` / `s8mk` (16x16 RGB+mask)
+ *     `il32` / `l8mk` (32x32 RGB+mask) -> plates the 16-32px range
+ *
+ * Dropping them leaves a perfectly valid family (ic07/ic08/ic09/ic10/ic11/ic13/
+ * ic14 — 32, 128, 256, 512 and 1024px), and macOS then renders cleanly at every
+ * size from 16px to 1024px. There is no visible quality cost: every small size
+ * is resampled from the 128px+ reps with high-quality interpolation.
+ *
+ * Note `tauri icon` re-emits all of these chunks on every run, which is why this
+ * post-processing step is committed rather than done once by hand. Always
+ * regenerate through `scripts/regenerate-icons.sh`, never with bare
+ * `tauri icon`.
+ *
+ * ## Usage
+ *
+ *   bun scripts/fix-icns.mjs [icns-path] [--keep-ic12]
+ *
+ * Defaults to desktop/src-tauri/icons/icon.icns. Edits the file in place and
+ * prints a before/after chunk summary.
+ */
+import { readFileSync, renameSync, writeFileSync } from "node:fs";
+import { dirname, resolve } from "node:path";
+import { fileURLToPath } from "node:url";
+
+const REPO_ROOT = resolve(dirname(fileURLToPath(import.meta.url)), "..");
+const DEFAULT_ICNS = "desktop/src-tauri/icons/icon.icns";
+
+// 16x16 / 32x32 RGB + 8-bit mask pairs. These predate macOS 10.7's PNG chunks
+// and are what IconServices uses for the smallest sizes.
+const LEGACY_CHUNKS = ["is32", "s8mk", "il32", "l8mk"];
+
+// 32x32@2x = 64x64. Legitimate modern chunk, but with legacy (padded) artwork
+// macOS plates it across the 40-64px range.
+const IC12 = "ic12";
+
+const args = process.argv.slice(2);
+const keepIc12 = args.includes("--keep-ic12");
+const pathArg = args.find((a) => !a.startsWith("-"));
+
+const unknown = args.filter((a) => a.startsWith("-") && a !== "--keep-ic12");
+if (unknown.length > 0) {
+  console.error(`fix-icns: unknown option(s): ${unknown.join(", ")}`);
+  console.error("usage: bun scripts/fix-icns.mjs [icns-path] [--keep-ic12]");
+  process.exit(2);
+}
+
+const target = resolve(REPO_ROOT, pathArg ?? DEFAULT_ICNS);
+
+/** Read an .icns container into its ordered chunks. */
+function readIcns(buf) {
+  if (buf.length < 8 || buf.toString("latin1", 0, 4) !== "icns") {
+    throw new Error(`not an .icns file: ${target}`);
+  }
+  const declared = buf.readUInt32BE(4);
+  if (declared !== buf.length) {
+    throw new Error(
+      `truncated/oversized .icns: header says ${declared} bytes, file is ${buf.length}`,
+    );
+  }
+  const chunks = [];
+  let offset = 8;
+  while (offset + 8 <= buf.length) {
+    const type = buf.toString("latin1", offset, offset + 4);
+    const size = buf.readUInt32BE(offset + 4);
+    if (size < 8 || offset + size > buf.length) {
+      throw new Error(
+        `corrupt .icns: chunk "${type}" at offset ${offset} declares ${size} bytes`,
+      );
+    }
+    chunks.push({ type, bytes: buf.subarray(offset, offset + size) });
+    offset += size;
+  }
+  return chunks;
+}
+
+function writeIcns(chunks) {
+  const body = Buffer.concat(chunks.map((c) => c.bytes));
+  const header = Buffer.alloc(8);
+  header.write("icns", 0, "latin1");
+  header.writeUInt32BE(body.length + 8, 4);
+  return Buffer.concat([header, body]);
+}
+
+const drop = new Set(LEGACY_CHUNKS);
+if (!keepIc12) drop.add(IC12);
+
+let original;
+try {
+  original = readFileSync(target);
+} catch (err) {
+  console.error(`fix-icns: cannot read ${target}: ${err.message}`);
+  process.exit(1);
+}
+
+let chunks;
+try {
+  chunks = readIcns(original);
+} catch (err) {
+  console.error(`fix-icns: ${err.message}`);
+  process.exit(1);
+}
+
+const before = chunks.map((c) => c.type);
+const kept = chunks.filter((c) => !drop.has(c.type));
+const removed = before.filter((t) => drop.has(t));
+
+if (removed.length === 0) {
+  console.log(`fix-icns: ${target} is already clean (no ${[...drop].join("/")} chunks)`);
+  process.exit(0);
+}
+
+if (kept.length === 0) {
+  console.error("fix-icns: refusing to write an icon family with no chunks left");
+  process.exit(1);
+}
+
+const out = writeIcns(kept);
+// Write to a sibling temp file then rename, so an interrupted run can't leave a
+// half-written icon in the tree.
+const tmp = `${target}.tmp`;
+writeFileSync(tmp, out);
+renameSync(tmp, target);
+
+console.log(`fix-icns: ${target}`);
+console.log(`  removed: ${removed.join(", ")}`);
+console.log(`  chunks:  ${kept.map((c) => c.type).join(", ")}`);
+console.log(`  ${original.length} -> ${out.length} bytes`);