Logging: structured slog messages throughout, and WithLogger options so callers choose the logger

Log messages are lower-case event names with their details as key/value
attributes ("error" for errors), in place of formatted strings.

Loggable package take a WithLogger option as part of their "New*" call,
defaulting to slog.Default(). Each tags its lines with its `component`.

Some debug loggers print directly rather than using slog when in
terminal logging mode.

internal/cli/version/command.go

@@ -16,13 +16,13 @@ func NewCommand() *cobra.Command {
 		Short:        "Print version information",
 		SilenceUsage: true,
 		PersistentPreRun: func(cmd *cobra.Command, args []string) {
-			slog.Debug("version.PersistentPreRun")
+			slog.Debug("command persistent pre-run", "command", "version")
 		},
 		PersistentPostRun: func(cmd *cobra.Command, args []string) {
-			slog.Debug("version.PersistentPostRun")
+			slog.Debug("command persistent post-run", "command", "version")
 		},
 		Run: func(cmd *cobra.Command, args []string) {
-			slog.Debug("version.Run")
+			slog.Debug("command run", "command", "version")
 
 			fmt.Printf("JobSearch - %s\n", version.Version)
 			if version.BuildTime != "unknown" {