Docs: Windows tiles for the plinth mark, and fix the UPLC diagram path

The tiles are rendered from the same POV-Ray scene as the favicons, keeping
their hard corners since Windows draws them as squares. assets/browserconfig.xml
overrides the one the TeXt theme ships, which pointed at the theme's own default
tiles and its own TileColor; a browserconfig.xml also takes precedence over the
msapplication-* meta tags, so it is what fixes the stale #ffc40d TileColor the
theme emits.

The UPLC boundary diagram was referenced as a bare absolute path, which drops
the baseurl the Pages workflow builds with -- the image 404'd on the deployed
site. Now goes through relative_url, as the wordmark on the front page does.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: hsyl20

_logo/make-icons.py

@@ -15,6 +15,10 @@
     android-chrome-192x192.png   192
     android-chrome-512x512.png   512
     favicon.ico                   16, 32, 48
+    mstile-70x70.png              70   Windows tiles, square corners
+    mstile-150x150.png           150
+    mstile-310x310.png           310
+    mstile-310x150.png           310x150, the wide tile
     <stem>-rounded.png          full size, for READMEs and slides
 """
 
@@ -36,6 +40,16 @@
 }
 ICO_SIZES = [(16, 16), (32, 32), (48, 48)]
 
+# Windows tiles. These keep their hard corners -- Windows draws them as squares
+# on a TileColor background -- so they come off the raw render, not the rounded
+# one. Only the sizes assets/browserconfig.xml actually references.
+TILE_SQUARES = {
+    "mstile-70x70.png": 70,
+    "mstile-150x150.png": 150,
+    "mstile-310x310.png": 310,
+}
+TILE_WIDE = ("mstile-310x150.png", 310, 150)
+
 
 def rounded_mask(size: int) -> Image.Image:
     big = size * SUPERSAMPLE
@@ -66,6 +80,22 @@ def main(argv: list[str]) -> int:
         tile.resize((size, size), Image.LANCZOS).save(out, optimize=True)
         written.append((out.name, size))
 
+    # Windows tiles, square and wide. The wide one is the square tile centred on
+    # a canvas of the tile colour, sampled from the render's own corner so the
+    # join is invisible.
+    square = Image.open(src).convert("RGB")
+    for name, size in TILE_SQUARES.items():
+        out = src.with_name(prefix + name)
+        square.resize((size, size), Image.LANCZOS).save(out, optimize=True)
+        written.append((out.name, size))
+
+    name, wide_w, wide_h = TILE_WIDE
+    canvas = Image.new("RGB", (wide_w, wide_h), square.getpixel((2, 2)))
+    canvas.paste(square.resize((wide_h, wide_h), Image.LANCZOS), ((wide_w - wide_h) // 2, 0))
+    out = src.with_name(prefix + name)
+    canvas.save(out, optimize=True)
+    written.append((out.name, f"{wide_w}x{wide_h}"))
+
     ico = src.with_name(prefix + "favicon.ico")
     tile.save(ico, sizes=ICO_SIZES)
     written.append((ico.name, ", ".join(str(w) for w, _ in ICO_SIZES)))

assets/browserconfig.xml

@@ -0,0 +1,20 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!-- Windows tile configuration, overriding the one the TeXt theme ships (which
+     points at the theme's own default tiles and its own TileColor). Tile images
+     here are rendered from the POV-Ray scene in _logo/.
+
+     src paths are resolved relative to this file, i.e. relative to /assets/, so
+     they are bare filenames and need no baseurl. Note also that when a
+     browserconfig.xml is present Windows ignores the msapplication-* meta tags,
+     which is how the theme's stale #ffc40d TileColor gets overridden. -->
+<browserconfig>
+  <msapplication>
+    <tile>
+      <square70x70logo src="mstile-70x70.png"/>
+      <square150x150logo src="mstile-150x150.png"/>
+      <wide310x150logo src="mstile-310x150.png"/>
+      <square310x310logo src="mstile-310x310.png"/>
+      <TileColor>#fc4d50</TileColor>
+    </tile>
+  </msapplication>
+</browserconfig>

assets/mstile-150x150.png

@@ -19,7 +19,7 @@ that it came from Plinth.
 
 ## The big picture
 
-![Plinth compiles Haskell source down to UPLC; everything after the UPLC boundary is shared by any UPLC script.](/assets/images/uplc-boundary.svg)
+![Plinth compiles Haskell source down to UPLC; everything after the UPLC boundary is shared by any UPLC script.]({{ '/assets/images/uplc-boundary.svg' | relative_url }})
 
 Above the boundary is language-specific. Below the boundary is where
 [other languages]({% link explanation/languages.md %}) — Plutarch, Aiken,