docs: a branding folder, and the three marks are not interchangeable

Shift is the logo, Guru is the icon, SchCotie is the mascot, and the difference
between them is not stylistic. An icon works once, at one size, in one state. A
mascot has to be able to *do* things -- confused, pleased, asleep, seen from
behind -- which is why it costs more and is drawn last. Written down because
this is exactly the kind of decision that gets re-derived badly.

Assets/ becomes docs/branding/, which also fixes two things:

  * Filenames had spaces in them, so every reference needed quoting. They are
    lowercase and hyphenated now.
  * Assets/ held hand-written SVG and generated PNG in one directory, which is
    the one rule docs/guides/layout.md states.

The guide records what was previously only in people's heads:

  * The constraint everything answers to -- include/logo.h is a 128x128
    single-channel coverage mask, so a mark has to survive as a solid shape in
    one colour and be recognisable at 24 px. Colour is the last decision, never
    the first.
  * Guru's purple is load-bearing. PSOGM_BG #4B1D9A is deliberately not the
    accent #7C5CFF, and theme.h's rule is that the full-bleed purple belongs
    entirely to failure. If Guru appears in accent violet on a sticker, the deep
    purple stops meaning "the machine stopped" -- and it is the only colour in
    the system that means anything.
  * Why shift-mask.svg is a separate file from shift.svg. mklogo.py reads ink as
    (255 - luminance) * alpha, so tones survive as coverage and the relationship
    inverts: darkest here is brightest on screen. Copying the violet fills would
    light the object from below.
  * Why a raster is committed beside its SVG. inkscape is not a build
    prerequisite, so requiring a vector rasteriser would break the build on most
    hosts for a file that changes about once a year.
  * That the BSD daemon is copyrighted and SchCotie must be drawn from the
    concept rather than from Beastie. A daemon is a Greek daimon and a Unix
    background process; neither is ownable. The pitchfork, the sneakers and that
    face are.

Format rule: SVG, or PNG at high resolution with no lossy compression, nothing
else. SVG is the source of truth for every mark and a raster is generated from
it, never edited.

include/logo.h regenerates byte-identical from the new path -- only the source
comment differs. The two old wordmark SVGs were deleted outside this session and
are left deleted; their PNGs are kept as superseded-*.png for reference.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VQ7Qx8E1q1M1bbCq8QLHS2

Makefile

@@ -1045,7 +1045,7 @@ qemu-schfs: esp $(BUILD)/schfs.img $(OVMF_CODE) $(OVMF_VARS)
 # The mark, not the wordmark. "SchOS Text Logo.png" is the text form and would
 # be illegible scaled to LOGO_PX; the small logo this used to name is gone,
 # replaced by the full logo, which is the same mark slightly redrawn.
-LOGO_SRC = Assets/SchOS Shift Mask.png
+LOGO_SRC = docs/branding/shift-mask.png
 LOGO_PX  = 128
 
 logo: