feat: update changelog (#131)

closes #130 

- CHANGELOG.md file for people who can view changelog from github
---
`iris changelog` command:
`iris changelog [version]` (e.g. iris changelog v0.5.1)
`iris changelog -n 3` (see changelog of 3 latest releaseas)

=> `iris changelog` looks just like CHANGELOG.md, grouped headers and
all. It only stops looking that way if we personally overwrite that
release's description with something else
=> With 1-hour local cache (invalidated on updater-channel change),
`--refresh` flag to bypass, graceful fallback to stale cache on GitHub
rate-limiting

---
- New auto update config
```toml
# 0 = off (default, notify only), 1 = auto-install, 2 = always confirm first
auto-update = 1
```

- New just debug-changelog and just debug-autoupdate recipes (fully
offline, mocked HTTP servers, no real network/config touched)

internal/config/config.go

@@ -61,6 +61,8 @@ type UpdaterConfig struct {
 	CheckOnStartup bool     `toml:"check-on-startup"`
 	Channel        string   `toml:"channel"`
 	CheckInterval  Duration `toml:"check-interval"`
+	// AutoUpdate: 0 = off (default), 1 = auto-install, 2 = always confirm first
+	AutoUpdate int `toml:"auto-update"`
 }
 
 type KeybindingsConfig struct {
@@ -281,6 +283,10 @@ func validate(cfg *Config) error {
 		return fmt.Errorf("updater.channel: invalid value %q (want: stable|nightly)", cfg.Updater.Channel)
 	}
 
+	if cfg.Updater.AutoUpdate < 0 || cfg.Updater.AutoUpdate > 2 {
+		return fmt.Errorf("updater.auto-update: invalid value %d (want: 0=off, 1=auto, 2=confirm)", cfg.Updater.AutoUpdate)
+	}
+
 	if cfg.UI.MaxSuggestions < 1 || cfg.UI.MaxSuggestions > 500 {
 		return fmt.Errorf("ui.max-suggestions: must be between 1 and 500")
 	}

internal/config/config_test.go

@@ -186,6 +186,24 @@ model = "qwen-2.5-coder-32b"
 	}
 }
 
+func TestValidateAutoUpdateRange(t *testing.T) {
+	cfg := DefaultConfig()
+
+	for _, valid := range []int{0, 1, 2} {
+		cfg.Updater.AutoUpdate = valid
+		if err := validate(cfg); err != nil {
+			t.Errorf("expected auto-update=%d to be valid, got error: %v", valid, err)
+		}
+	}
+
+	for _, invalid := range []int{-1, 3} {
+		cfg.Updater.AutoUpdate = invalid
+		if err := validate(cfg); err == nil {
+			t.Errorf("expected auto-update=%d to be rejected", invalid)
+		}
+	}
+}
+
 func TestLoadSave(t *testing.T) {
 	tmpDir, err := os.MkdirTemp("", "iris-config-test")
 	if err != nil {

internal/config/defaults.go

@@ -32,6 +32,7 @@ func DefaultConfig() *Config {
 			CheckOnStartup: true,
 			Channel:        "stable",
 			CheckInterval:  Duration(24 * time.Hour),
+			AutoUpdate:     0,
 		},
 		AI: AIConfig{
 			Enabled:       false,
@@ -59,8 +60,11 @@ func DefaultState() *State {
 	return &State{
 		LastMode: "spec",
 		Updater: UpdaterState{
-			LastCheckTime: time.Time{},
-			SeenVersion:   "",
+			LastCheckTime:     time.Time{},
+			SeenVersion:       "",
+			AutoUpdateTarget:  "",
+			AutoUpdateAttempt: 0,
+			DeclinedVersion:   "",
 		},
 	}
 }

internal/config/state.go

@@ -11,6 +11,10 @@ import (
 type UpdaterState struct {
 	LastCheckTime time.Time `toml:"last-check-time"`
 	SeenVersion   string    `toml:"seen-version"`
+	// auto-update escalation ladder state, see decideAutoUpdateAction
+	AutoUpdateTarget  string `toml:"auto-update-target"`
+	AutoUpdateAttempt int    `toml:"auto-update-attempt"`
+	DeclinedVersion   string `toml:"declined-version"`
 }
 
 type State struct {