win: give the executable an icon and a version block

[vstrelnikof]

What was wrong

Installed from the MSI, PolterType sits in the Start menu wearing the
shell's placeholder. Measured on the installed binary:

icon groups in installed exe: 0
FileVersion  = []
ProductName  = []
Shortcut icon = [,0]

Zero icon resources, no VERSIONINFO at all, and a shortcut whose
IconLocation is ,0 — "ask the target file". The target had nothing
to give.

The only icon we ever produced was the installer's, and
ARPPRODUCTICON reaches exactly one screen: Add/Remove Programs.
Explorer, Alt-Tab, the taskbar and every pinned entry were in the same
position, and the Settings window had no icon of its own either.

What this does

poltertype-app gains a build script that renders an .ico into
OUT_DIR and hands it to rc.exe via winresource, together with a
VERSIONINFO block naming the product rather than the crate. The WiX
template is untouched — the shortcut inherits the icon because the
fix is upstream of the installer.

The mark is rendered, not checked in. The geometry moves out of xtask
into a new poltertype-icon crate, so the build script, the installers
and the Settings window all draw from one source and cannot drift. It is
a build-dependency of the app; nothing in it is linked into the shipped
binary except the 64 px window icon.

Release CI drops ImageMagick with it: cargo xtask assets icon-ico
rasterises every size from the vector mark instead of box-filtering one
1024 px master.

Verified on real Windows, through the shell's own APIs

Check	Before	After
ExtractIconEx(exe, -1)	0 icon groups	1
VersionInfo.ProductName	empty	PolterType
GDI+ new Icon(ico, N, N)	—	all six sizes load at their exact size
SHGetFileInfo on an MSI-style shortcut	placeholder	draws the mark
Settings window WM_GETICON	0	a 64 px copy

The .ico is 113 KB: 16/32/48/64/128 as DIBs, 256 PNG-compressed.

Notes for review

• The build script tests CARGO_CFG_TARGET_OS, not cfg! — a build
  script runs on the machine doing the building, and the question is
  about the machine that will run the binary. That also keeps
  poltertype-app at zero #[cfg(target_os)].
• ico/tests.rs reads the container back the way Windows does. A
  wrong offset table produces a file that parses and that the shell
  silently declines to draw, which is indistinguishable from the bug
  being fixed.
• cargo deny is not installed on the machine this was written on, so
  the new dependencies' licences were checked by hand against
  deny.toml: winresource MIT, toml/serde_spanned/toml_writer
  MIT OR Apache-2.0.