Step 11 of the gui/app.py + gui/preview.py structural refactor. Pure
copy: the toggleable info panel widget with category-coloured tag
list moves to its own module. The new module gets its own
`log = logging.getLogger("booru")` at module level — same logger
instance the rest of the app uses (logging.getLogger is idempotent
by name), matching the existing per-module convention used by
grid.py / bookmarks.py / library.py. All six tag-color Qt Properties
preserved verbatim. app.py grows another shim line. Shim removed
in commit 14.
