feat(mc): open files with their configured app via xdg-open

Ship `mc.ext.ini` as the `local.mc.extIni` option (like `local.mc.menu`):
Enter browses archives in-place as before and delegates every other type to
`xdg-open`. Add public `mime.nix` with `xdg.mimeApps` defaults (pdf ->
zathura, images -> imv, audio/video -> mpv, office -> libreoffice) -- public
because those handlers are; personal browser/mail defaults stay private.

Also document, at the Hyprland swallow config, how swallowing differs from an
app opening fullscreen/maximized (LibreOffice restores its own maximized state
and looks swallowed but isn't).

modules/assets/mc/mc.ext.ini

@@ -0,0 +1,81 @@
+# Midnight Commander file associations (public baseline).
+#
+# mc reads a SINGLE mc.ext.ini; this user copy fully replaces the system one
+# (they are not merged), so it must also carry the archive entries we keep.
+#
+# Policy: Enter (Open) on an archive mounts it as a virtual filesystem (mc
+# built-in, no external helper). Every other file falls through to [Default],
+# which runs `xdg-open` -- so the app is whatever the XDG mimeapps default
+# resolves to (set those in the private inventory's xdg.mimeApps). One source of
+# truth, shared with every other launcher; nothing app-specific baked in here.
+#
+# Note: office documents (.docx/.odt/.xlsx/...) are ZIP containers, so they are
+# deliberately absent from the [zip] entry below -- otherwise Enter would mount
+# them as archives instead of handing them to LibreOffice via xdg-open.
+#
+# Override contract (this is a types.lines option shipped as mkBefore): append a
+# same-named section to override one key -- mc merges same-named sections and
+# the last key wins -- e.g. add a [Default] with a different Open to change the
+# fallback, or add [pdf] Type=^PDF / Open=mupdf %f & to force one type to a
+# specific app. lib.mkForce "..." replaces this baseline wholesale.
+
+[mc.ext.ini]
+Version=4.0
+
+### Archives: Enter mounts them as a virtual filesystem (F3/F4 unaffected) ###
+
+[tar]
+Regex=\\.(tar(\\.(gz|bz2|xz|zst|lz|lz4|lzo|Z))?|t(gz|az|bz2?|xz|zst|lz))$
+Open=%cd %p/utar://
+
+[zip]
+Regex=\\.(zip|jar|xpi|whl|egg|apk|war|ear)$
+Open=%cd %p/uzip://
+
+[7z]
+Shell=.7z
+Open=%cd %p/u7z://
+
+[rar]
+Regex=\\.r(ar|[0-9][0-9])$
+Open=%cd %p/urar://
+
+[arj]
+Regex=\\.a(rj|[0-9][0-9])$
+Open=%cd %p/uarj://
+
+[cab]
+Shell=.cab
+Open=%cd %p/ucab://
+
+[cpio]
+Regex=\\.cpio(\\.(gz|xz|bz2|zst|lz|lz4|lzo|Z))?$
+Open=%cd %p/ucpio://
+
+[deb]
+Regex=\\.u?deb$
+Open=%cd %p/deb://
+
+[rpm]
+Regex=\\.(rpm|src\\.rpm|spm)$
+Open=%cd %p/rpm://
+
+[iso]
+Shell=.iso
+Open=%cd %p/iso9660://
+
+[patch]
+Regex=\\.(diff|patch)(\\.(gz|bz2|xz|zst|Z))?$
+Open=%cd %p/patchfs://
+
+### Everything else: hand off to the desktop's configured default app ###
+
+# `&` backgrounds xdg-open so mc's shell returns and the launched GUI is orphaned
+# to init. Hyprland only swallows the terminal when the new window's parent-PID
+# chain still has a foot ancestor (getSwallower in Hyprland's Window.cpp), so an
+# orphaned app opens as its own tile instead of swallowing mc (zathura, imv, ...).
+# %f MUST stay unquoted: mc already backslash-escapes the path, so quoting turns
+# those backslashes literal and breaks filenames with spaces.
+
+[Default]
+Open=xdg-open %f &