feat(cd): optionally complete from zoxide's database

`cd` completes from FileGenerator, which reads one directory: the one you
are standing in. So `cd proj` only ever resolves when proj happens to be
a child of the current directory, and returns nothing at all otherwise --
including for directories visited constantly. That is the opposite of
what cd is normally reached for, and it reads as completion being broken
rather than as a scope limit.

zoxide.extend-cd routes `cd` through the generator `z` already uses, so
local children are offered first and zoxide's frecency database fills in
everything else, reachable by name from anywhere.

Off by default: it shells out to zoxide, and offering absolute paths from
outside the current directory is a real change in what `cd` proposes.

The query is also cached for two seconds. Generators run on every
keystroke and `zoxide query -l` is a subprocess costing ~11ms here, which
is the whole redraw budget; the list only changes when the user changes
directory, so the window costs nothing. This applies to `z` and `zi` too,
which were paying it per keystroke already.

internal/config/defaults.go

@@ -47,6 +47,9 @@ func DefaultConfig() *Config {
 				MinIntervalMS: 5000,
 			},
 		},
+		Zoxide: ZoxideConfig{
+			ExtendCd: false,
+		},
 		Keybindings: KeybindingsConfig{
 			ToggleMode:       "ctrl+r",
 			ToggleMenu:       "shift+tab",