cli: implement --config flag to load TOML config file

The --config flag was registered but silently ignored. Now:
- config.LoadFile loads a TOML file on top of defaults
- PersistentPreRunE applies the file when --config is set
- Explicit CLI flags (--data-dir, --claude-bin) take precedence over the file

Tests: TestLoadFile_OverridesDefaults, TestLoadFile_MissingFile_ReturnsError,
TestRootCmd_ConfigFile_Loaded, TestRootCmd_ConfigFile_CLIFlagOverrides,
TestRootCmd_ConfigFile_Missing_ReturnsError

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

1 files changed, 19 insertions, 0 deletions

diff --git a/internal/cli/root.go b/internal/cli/root.go
index ab6ac1f..7c4f2ff 100644
--- a/internal/cli/root.go
+++ b/internal/cli/root.go
@@ -38,7 +38,26 @@ func NewRootCmd() *cobra.Command {
 	cmd.PersistentFlags().BoolVarP(&verbose, "verbose", "v", false, "verbose output")
 
 	// Re-derive DBPath and LogDir after flags are parsed, so --data-dir takes effect.
+	// If --config is provided, load that file first; explicit CLI flags override it.
 	cmd.PersistentPreRunE = func(cmd *cobra.Command, args []string) error {
+		if cfgFile != "" {
+			// Save values set by explicit CLI flags before overwriting cfg from file.
+			flagDataDir := cfg.DataDir
+			flagClaudeBin := cfg.ClaudeBinaryPath
+
+			loaded, err := config.LoadFile(cfgFile)
+			if err != nil {
+				return err
+			}
+			*cfg = *loaded
+
+			if cmd.Flags().Changed("data-dir") {
+				cfg.DataDir = flagDataDir
+			}
+			if cmd.Flags().Changed("claude-bin") {
+				cfg.ClaudeBinaryPath = flagClaudeBin
+			}
+		}
 		cfg.DBPath = filepath.Join(cfg.DataDir, "claudomator.db")
 		cfg.LogDir = filepath.Join(cfg.DataDir, "executions")
 		return nil