core: fix security and concurrency issues found in a backend audit (#2805)

* core: fix security and concurrency issues found in backend audit

Security:
- privesc: pipe the sudo password via stdin (sudo -S) instead of
  embedding it in the command string, so it no longer appears in argv
  (readable by any local user via /proc/<pid>/cmdline or ps)
- greeter: tokenize a session .desktop Exec= line into argv and execve
  directly instead of running it through /bin/sh -c, closing a command-
  injection path via user-writable ~/.local/share/wayland-sessions
- plugins: reject path-separator/.. in plugin id/name before joining
  into a filesystem path, closing an arbitrary-directory-delete in the
  uninstall/update fallback
- keybinds/hyprland: always quote unrecognized bind actions/keys when
  writing generated Lua; only re-emit genuine round-tripped custom Lua
  verbatim (tracked via an explicit flag), closing a Lua-injection path
- desktop/mimeapps: reject newline/bracket in mime/desktop-id fields so
  they can't inject fake sections into the shared mimeapps.list

Robustness / concurrency:
- server: recover panics in the request-dispatch path so one bad
  handler can't crash the daemon and drop every client
- go-wayland: recover panics in the shared dispatch choke point so a
  malformed compositor event can't crash CLI tools / the daemon
- server: per-connection D-Bus client ID instead of a shared constant,
  fixing cross-client signal delivery and subscription teardown
- network: guard the NetworkManager device maps with a mutex (a
  concurrent map read/write here is an unrecoverable fatal error)
- cups: close the event channel on Stop() so Unsubscribe() of the last
  subscriber no longer deadlocks; allocate the fresh channel in Start()
- freedesktop: reuse the shared session conn for the settings watcher
  and tear it down in Close(), fixing a per-Manager conn+goroutine leak
- clipboard: mutex-guard lazy dbusConn creation
- geolocation: use WithMatchMember for the GeoClue2 LocationUpdated
  signal (was WithMatchSender with an interface.member string, so the
  match never fired and live location updates never arrived)
- screenshot: set failed=true on buffer/pool creation errors so the
  dispatch loop doesn't wait forever for a ready/failed that never comes

* apply code review comments

---------

Co-authored-by: bbedward <bbedward@gmail.com>
(cherry picked from commit ca89e12963)

core/pkg/go-wayland/wayland/client/context.go

@@ -96,7 +96,7 @@ func (ctx *Context) GetDispatch() func() error {
 		}
 	}
 
-	return func() error {
+	return func() (dispatchErr error) {
 		proxy, ok := ctx.objects.Load(senderID)
 		if !ok {
 			return nil // Proxy already deleted via delete_id, silently ignore
@@ -111,6 +111,14 @@ func (ctx *Context) GetDispatch() func() error {
 			return fmt.Errorf("%w (senderID=%d)", ErrDispatchSenderUnsupported, senderID)
 		}
 
+		// generated Dispatch methods don't bounds-check wire data; surface a
+		// decoder panic as an error instead of crashing the process
+		defer func() {
+			if r := recover(); r != nil {
+				dispatchErr = fmt.Errorf("dispatch: panic handling opcode=%d senderID=%d: %v", opcode, senderID, r)
+			}
+		}()
+
 		sender.Dispatch(opcode, fd, data)
 		return nil
 	}