Add testable CLI with dependency injection and new scanner/checker packages

Major changes:
- Refactor CLI to accept injected I/O streams and filesystem (afero.Fs)
  for testing without touching the real filesystem
- Add RunOptions struct and RunWithOptions() for configurable CLI execution
- Add internal/scanner package with two-phase manifest generation:
  - Phase 1 (Enumeration): walk directories, collect metadata
  - Phase 2 (Scan): read contents, compute hashes, write manifest
- Add internal/checker package for manifest verification with progress
  reporting and channel-based result streaming
- Add mfer/builder.go for incremental manifest construction
- Add --no-extra-files flag to check command to detect files not in manifest
- Add timing summaries showing file count, size, elapsed time, and throughput
- Add comprehensive tests using afero.MemMapFs (no real filesystem access)
- Add contrib/usage.sh integration test script
- Fix banner ASCII art alignment (consistent spacing)
- Fix verbosity levels so summaries display at default log level
- Update internal/log to support configurable output writers

internal/cli/mfer.go

@@ -2,9 +2,11 @@ package cli
 
 import (
 	"fmt"
+	"io"
 	"os"
 	"time"
 
+	"github.com/spf13/afero"
 	"github.com/urfave/cli/v2"
 	"sneak.berlin/go/mfer/internal/log"
 )
@@ -16,22 +18,31 @@ type CLIApp struct {
 	startupTime time.Time
 	exitCode    int
 	app         *cli.App
+
+	// I/O streams - all program input/output should go through these
+	Stdin  io.Reader
+	Stdout io.Writer
+	Stderr io.Writer
+
+	// Fs is the filesystem abstraction - defaults to OsFs for real filesystem
+	Fs afero.Fs
 }
 
-const banner = `              ___           ___         ___           ___
-	     /__/\         /  /\       /  /\         /  /\
-	    |  |::\       /  /:/_     /  /:/_       /  /::\
-	    |  |:|:\     /  /:/ /\   /  /:/ /\     /  /:/\:\
-	  __|__|:|\:\   /  /:/ /:/  /  /:/ /:/_   /  /:/~/:/
-	 /__/::::| \:\ /__/:/ /:/  /__/:/ /:/ /\ /__/:/ /:/___
-	 \  \:\~~\__\/ \  \:\/:/   \  \:\/:/ /:/ \  \:\/:::::/
-	  \  \:\        \  \::/     \  \::/ /:/   \  \::/~~~~
-	   \  \:\        \  \:\      \  \:\/:/     \  \:\
-	    \  \:\        \  \:\      \  \::/       \  \:\
-	     \__\/         \__\/       \__\/         \__\/`
+const banner = `
+     ___           ___         ___           ___
+    /__/\         /  /\       /  /\         /  /\
+   |  |::\       /  /:/_     /  /:/_       /  /::\
+   |  |:|:\     /  /:/ /\   /  /:/ /\     /  /:/\:\
+ __|__|:|\:\   /  /:/ /:/  /  /:/ /:/_   /  /:/~/:/
+/__/::::| \:\ /__/:/ /:/  /__/:/ /:/ /\ /__/:/ /:/___
+\  \:\~~\__\/ \  \:\/:/   \  \:\/:/ /:/ \  \:\/:::::/
+ \  \:\        \  \::/     \  \::/ /:/   \  \::/~~~~
+  \  \:\        \  \:\      \  \:\/:/     \  \:\
+   \  \:\        \  \:\      \  \::/       \  \:\
+    \__\/         \__\/       \__\/         \__\/`
 
 func (mfa *CLIApp) printBanner() {
-	fmt.Println(banner)
+	fmt.Fprintln(mfa.Stdout, banner)
 }
 
 func (mfa *CLIApp) VersionString() string {
@@ -47,7 +58,7 @@ func (mfa *CLIApp) setVerbosity(v int) {
 	}
 }
 
-func (mfa *CLIApp) run() {
+func (mfa *CLIApp) run(args []string) {
 	mfa.startupTime = time.Now()
 
 	if NO_COLOR {
@@ -55,6 +66,8 @@ func (mfa *CLIApp) run() {
 		log.DisableStyling()
 	}
 
+	// Configure log package to use our I/O streams
+	log.SetOutput(mfa.Stdout, mfa.Stderr)
 	log.Init()
 
 	var verbosity int
@@ -64,6 +77,8 @@ func (mfa *CLIApp) run() {
 		Usage:                "Manifest generator",
 		Version:              mfa.VersionString(),
 		EnableBashCompletion: true,
+		Writer:               mfa.Stdout,
+		ErrWriter:            mfa.Stderr,
 		Flags: []cli.Flag{
 			&cli.BoolFlag{
 				Name:    "verbose",
@@ -106,11 +121,17 @@ func (mfa *CLIApp) run() {
 						Aliases: []string{"o"},
 						Usage:   "Specify output filename",
 					},
+					&cli.BoolFlag{
+						Name:    "progress",
+						Aliases: []string{"P"},
+						Usage:   "Show progress during enumeration and scanning",
+					},
 				},
 			},
 			{
-				Name:  "check",
-				Usage: "Validate files using manifest file",
+				Name:      "check",
+				Usage:     "Validate files using manifest file",
+				ArgsUsage: "[manifest file]",
 				Action: func(c *cli.Context) error {
 					if !c.Bool("quiet") {
 						mfa.printBanner()
@@ -118,12 +139,29 @@ func (mfa *CLIApp) run() {
 					mfa.setVerbosity(verbosity)
 					return mfa.checkManifestOperation(c)
 				},
+				Flags: []cli.Flag{
+					&cli.StringFlag{
+						Name:    "base",
+						Aliases: []string{"b"},
+						Value:   ".",
+						Usage:   "Base directory for resolving relative paths from manifest",
+					},
+					&cli.BoolFlag{
+						Name:    "progress",
+						Aliases: []string{"P"},
+						Usage:   "Show progress during checking",
+					},
+					&cli.BoolFlag{
+						Name:  "no-extra-files",
+						Usage: "Fail if files exist in base directory that are not in manifest",
+					},
+				},
 			},
 			{
 				Name:  "version",
 				Usage: "Show version",
 				Action: func(c *cli.Context) error {
-					fmt.Printf("%s\n", mfa.VersionString())
+					fmt.Fprintln(mfa.Stdout, mfa.VersionString())
 					return nil
 				},
 			},
@@ -142,7 +180,7 @@ func (mfa *CLIApp) run() {
 	}
 
 	mfa.app.HideVersion = true
-	err := mfa.app.Run(os.Args)
+	err := mfa.app.Run(args)
 	if err != nil {
 		mfa.exitCode = 1
 		log.WithError(err).Debugf("exiting")