feat(config): ui width, auto exec, selection and navigation configs (#80)

closes #67

So I made an auto-exec confg `auto-exec = true`
(e32c0ba6ed69f3c764353e58b8fbacf160f37d5a) which means:
- If you want your command in the prompt to be executed right away, you
can set this = false (for example, you are typing `nvim ~/.conf` but
IRIS is suggesting `nvim ~/.config`, it will ignore the suggestion and
exec what you are typing, this is current default behavior)
- If you want to auto execute full command which is being suggested, you
can set this = true (this is the opposite of above, when you are typing
`nvim ~/.conf` but IRIS is suggesting `nvim ~/.config`, it will auto
exec `nvim ~/.config` instead, but sometime you want to exec what you
are typing instead of the suggestion right?, just press esc or shift tab
to hide the menu and it will)

---

Select keybinding to replace tab
(0dc01cba8c610e8d6fd8c50f6a71bdcc061a098f)
`select = "ctrl+y"`

Some users may love nvim keybinding or emacs, so I bring navigation
keybinding to be configurable (0dc01cba8c610e8d6fd8c50f6a71bdcc061a098f)
```
navigate-up = "ctrl+k"
navigate-down = "ctrl+j"
```
---

I also added a option for UI width
(dfa3b810a7be406fe4652b3886020f37bb166811)
`max-width = 80`
- If you configure `max-width` to be larger than the actual width of the
current terminal, Iris will automatically "compress" the window to match
the terminal's width (meaning it will never overflow and break the
interface)
- If you configure `max-width` too small (e.g 10), the interface will
have cramped text, making it look very bad. So, I've set a minimum safe
min limit of 40. If the configured value is smaller than this, Iris will
automatically use 40

Small note: If you set `max-width = 0` (or leave it blank), it will
automatically use Iris's default standard size of 76. SO you can
confidently customize it without fear of breaking the UI (I hope so
lmao)

---

Added a fallback to ensure Iris never crashes or loses shortcuts if the
user accidentally deletes keybinding configuration lines or
intentionally assigns empty strings " "
(f682c9bf623f3ed46ad0763221145604dbd91b07)

Fix typo `toggle_mode` to `toggle-mode`
(b39be6673e552735fa65a6c9807510c83b4d9cdd)

if you have a better config design, please tell me, I always listen to
your idea

internal/config/config.go

@@ -39,6 +39,7 @@ type CoreConfig struct {
 	Mode        string `toml:"mode"`
 	Debug       bool   `toml:"debug"`
 	ExpandAlias bool   `toml:"expand-alias"`
+	AutoExecute bool   `toml:"auto-execute"`
 }
 
 type UIConfig struct {
@@ -47,6 +48,7 @@ type UIConfig struct {
 	ShowHiddenFiles bool   `toml:"hidden-files"`
 	MaxSuggestions  int    `toml:"max-suggestions"`
 	MaxHeight       int    `toml:"max-height"`
+	MaxWidth        int    `toml:"max-width"`
 	NerdFonts       bool   `toml:"nerd-fonts"`
 }
 
@@ -62,8 +64,11 @@ type UpdaterConfig struct {
 }
 
 type KeybindingsConfig struct {
-	ToggleMode string `toml:"toggle-mode"`
-	ToggleMenu string `toml:"toggle-menu"`
+	ToggleMode       string `toml:"toggle-mode"`
+	ToggleMenu       string `toml:"toggle-menu"`
+	SelectSuggestion string `toml:"select"`
+	NavigateUp       string `toml:"navigate-up"`
+	NavigateDown     string `toml:"navigate-down"`
 }
 
 type SuggestOnEmptyConfig struct {
@@ -186,6 +191,23 @@ func Load() (*Config, error) {
 
 	applyEnv(cfg)
 
+	// fallback for empty keybindings
+	if cfg.Keybindings.ToggleMode == "" {
+		cfg.Keybindings.ToggleMode = "ctrl+r"
+	}
+	if cfg.Keybindings.ToggleMenu == "" {
+		cfg.Keybindings.ToggleMenu = "shift+tab"
+	}
+	if cfg.Keybindings.SelectSuggestion == "" {
+		cfg.Keybindings.SelectSuggestion = "tab"
+	}
+	if cfg.Keybindings.NavigateUp == "" {
+		cfg.Keybindings.NavigateUp = "up"
+	}
+	if cfg.Keybindings.NavigateDown == "" {
+		cfg.Keybindings.NavigateDown = "down"
+	}
+
 	if err := validate(cfg); err != nil {
 		return cfg, fmt.Errorf("config: invalid value: %w", err)
 	}