refactor: group stow packages into common, mac and kde

Split the packages by platform so each app stays an opt-in Stow package
under common/, mac/ or kde/. KDE gets its own Fastfetch, Helium and
Spectacle packages, and darwin-breeze becomes kde/theme. The READMEs
document stowing a whole group as well as individual packages.

kde/fastfetch/build.py

@@ -0,0 +1,57 @@
+#!/usr/bin/env python3
+"""Encode albedo.png as kitty graphics escapes for fastfetch's "raw" logo.
+
+fastfetch's "kitty-direct" logo sends the terminal a file path (t=f). Konsole
+only accepts inline data (t=d) and answers t=f with ENOTSUPPORTED, which lands
+on the prompt as typed input. These files carry the PNG inline instead, with
+q=2 so the terminal never answers at all.
+
+  .config/fastfetch/albedo-konsole.kitty   pre-scaled for Konsole
+
+Konsole stretches the image to the c x r cell box with nearest-neighbour
+scaling, at logical (not device) pixel size, so a 512px source turns grainy.
+The Konsole copy is resized with Lanczos to exactly that box, which leaves
+Konsole nothing to scale. Rerun after changing the image, the logo size or the
+Konsole font.
+"""
+
+import base64
+import subprocess
+import tempfile
+from pathlib import Path
+
+PKG = Path(__file__).resolve().parent
+DIR = PKG / ".config/fastfetch"
+SOURCE = DIR / "albedo.png"
+# Logo size in cells; keep in sync with "width" and "height" in config.jsonc.
+COLS, ROWS = 20, 10
+# Konsole's cell size in logical pixels for JetBrainsMono Nerd Font 10pt
+# (QFontMetrics: average advance of Konsole's REPCHAR, and height()).
+KONSOLE_CELL = 8, 17
+
+
+def encode(png, dst):
+    data = base64.b64encode(png)
+    chunks = [data[i : i + 4096] for i in range(0, len(data), 4096)]
+    out = bytearray()
+    for n, chunk in enumerate(chunks):
+        more = int(n < len(chunks) - 1)
+        if n == 0:
+            keys = b"a=T,f=100,t=d,c=%d,r=%d,q=2,m=%d" % (COLS, ROWS, more)
+        else:
+            keys = b"m=%d" % more
+        out += b"\x1b_G" + keys + b";" + chunk + b"\x1b\\"
+    dst.write_bytes(out)
+
+
+def resize(width, height):
+    with tempfile.TemporaryDirectory() as tmp:
+        out = Path(tmp) / "out.png"
+        subprocess.run(
+            ["vipsthumbnail", SOURCE, "--size", f"{width}x{height}!", "-o", out],
+            check=True,
+        )
+        return out.read_bytes()
+
+
+encode(resize(COLS * KONSOLE_CELL[0], ROWS * KONSOLE_CELL[1]), DIR / "albedo-konsole.kitty")