Initial commit: unitdore scaffold + syncup/edit commands

- config: load/save/add unit, Unit struct
- runtime: podman + docker discovery and exists check
- cmd: syncup (discover + reconcile), edit, cobra root
- PLAN.md: full project plan

config/config.go

@@ -0,0 +1,85 @@
+package config
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+
+	"gopkg.in/yaml.v3"
+)
+
+const DefaultConfigPath = "/etc/unitdore/units.yaml"
+
+// Unit represents a single managed container unit.
+type Unit struct {
+	Name           string `yaml:"name"`
+	Runtime        string `yaml:"runtime"`         // podman | docker | exec
+	User           string `yaml:"user,omitempty"`  // empty = root/system unit
+	Command        string `yaml:"command,omitempty"` // override ExecStart
+	Order          int    `yaml:"order"`
+	Delay          string `yaml:"delay,omitempty"` // e.g. "5s"
+	Enabled        bool   `yaml:"enabled"`
+	DisabledReason string `yaml:"disabled_reason,omitempty"`
+}
+
+// Config is the root config structure.
+type Config struct {
+	Units []Unit `yaml:"units"`
+}
+
+// Load reads and parses the config file at path.
+func Load(path string) (*Config, error) {
+	data, err := os.ReadFile(path)
+	if err != nil {
+		return nil, fmt.Errorf("reading config: %w", err)
+	}
+	var cfg Config
+	if err := yaml.Unmarshal(data, &cfg); err != nil {
+		return nil, fmt.Errorf("parsing config: %w", err)
+	}
+	return &cfg, nil
+}
+
+// LoadOrEmpty loads the config file, or returns an empty config if it doesn't exist.
+func LoadOrEmpty(path string) (*Config, error) {
+	_, err := os.Stat(path)
+	if os.IsNotExist(err) {
+		return &Config{}, nil
+	}
+	return Load(path)
+}
+
+// Save writes the config back to disk, creating parent directories if needed.
+func (c *Config) Save(path string) error {
+	if err := os.MkdirAll(filepath.Dir(path), 0755); err != nil {
+		return fmt.Errorf("creating config dir: %w", err)
+	}
+	data, err := yaml.Marshal(c)
+	if err != nil {
+		return fmt.Errorf("marshalling config: %w", err)
+	}
+	if err := os.WriteFile(path, data, 0644); err != nil {
+		return fmt.Errorf("writing config: %w", err)
+	}
+	return nil
+}
+
+// FindUnit returns a pointer to the unit with the given name, or nil.
+func (c *Config) FindUnit(name string) *Unit {
+	for i := range c.Units {
+		if c.Units[i].Name == name {
+			return &c.Units[i]
+		}
+	}
+	return nil
+}
+
+// AddUnit appends a unit if one with that name doesn't already exist.
+// Returns true if it was added.
+func (c *Config) AddUnit(u Unit) bool {
+	if c.FindUnit(u.Name) != nil {
+		return false
+	}
+	c.Units = append(c.Units, u)
+	return true
+}