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/config.go

@@ -78,6 +78,21 @@ type KeybindingsConfig struct {
 	NavigateRight    string `toml:"navigate-right"`
 }
 
+type ZoxideConfig struct {
+	// ExtendCd adds zoxide's frecency database to `cd` completions.
+	//
+	// Without it `cd` only offers direct children of the current directory,
+	// because that is all the file generator walks -- so `cd proj` finds
+	// nothing unless you are already standing in the parent. With it, any
+	// directory zoxide has seen is reachable by name from anywhere, which is
+	// what `cd` is usually wanted for.
+	//
+	// Off by default: it shells out to zoxide, and the suggestions are absolute
+	// paths from outside the current directory, which is a real change in what
+	// `cd` offers.
+	ExtendCd bool `toml:"extend-cd"`
+}
+
 type SuggestOnEmptyConfig struct {
 	Enabled       bool `toml:"enabled"`
 	DebounceMS    int  `toml:"debounce_ms"`
@@ -127,6 +142,7 @@ type Config struct {
 	Git         GitConfig         `toml:"git"`
 	Updater     UpdaterConfig     `toml:"updater"`
 	AI          AIConfig          `toml:"ai"`
+	Zoxide      ZoxideConfig      `toml:"zoxide"`
 	Keybindings KeybindingsConfig `toml:"keybindings"`
 }