feat: auto-install ffmpeg and yt-dlp during GUI installation

Add "Installing media tools" step to the installer that automatically
installs ffmpeg and yt-dlp if not already present on the system.
Uses winget (Windows), Homebrew (macOS), or apt-get (Linux).
Non-critical step — installation continues even if this fails.

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

edge-ai-platform/installer/app.go

@@ -231,7 +231,8 @@ func (inst *Installer) runInstall(config InstallConfig) {
 		{"Extracting scripts", 48, true, inst.stepExtractScripts},
 		{"Configuring system", 55, false, inst.stepConfigureSystem},
 		{"Setting up USB driver", 62, false, inst.stepSetupLibusb},
-		{"Setting up Python environment", 72, false, inst.stepSetupPython},
+		{"Setting up Python environment", 70, false, inst.stepSetupPython},
+		{"Installing media tools", 78, false, inst.stepInstallFfmpeg},
 		{"Writing configuration", 85, true, inst.stepWriteConfig},
 		{"Verifying installation", 90, false, inst.stepVerify},
 		{"Setting up auto-start launcher", 95, false, inst.stepAutoRestart},
@@ -519,6 +520,24 @@ func (inst *Installer) setupPythonVenv(installDir string) error {
 	return nil
 }
 
+func (inst *Installer) stepInstallFfmpeg(config InstallConfig) error {
+	needFfmpeg := true
+	if _, err := exec.LookPath("ffmpeg"); err == nil {
+		needFfmpeg = false
+	}
+
+	needYtdlp := true
+	if _, err := exec.LookPath("yt-dlp"); err == nil {
+		needYtdlp = false
+	}
+
+	if !needFfmpeg && !needYtdlp {
+		return nil // both already installed
+	}
+
+	return installFfmpeg(inst, needFfmpeg, needYtdlp)
+}
+
 func (inst *Installer) stepWriteConfig(config InstallConfig) error {
 	cfgDir := platformConfigDir()
 	if err := os.MkdirAll(cfgDir, 0755); err != nil {

edge-ai-platform/installer/platform_darwin.go

@@ -138,6 +138,39 @@ func installAutoRestart(installDir string) error {
 	return nil
 }
 
+func installFfmpeg(inst *Installer, needFfmpeg, needYtdlp bool) error {
+	if _, err := exec.LookPath("brew"); err != nil {
+		return fmt.Errorf("Homebrew not found — install from https://brew.sh then run: brew install ffmpeg")
+	}
+
+	if needFfmpeg {
+		inst.emitProgress(ProgressEvent{
+			Step:    "ffmpeg",
+			Message: "Installing ffmpeg via Homebrew (this may take a few minutes)...",
+			Percent: 79,
+		})
+		cmd := exec.Command("brew", "install", "ffmpeg")
+		if out, err := cmd.CombinedOutput(); err != nil {
+			return fmt.Errorf("brew install ffmpeg failed: %s — %w", string(out), err)
+		}
+	}
+
+	if needYtdlp {
+		inst.emitProgress(ProgressEvent{
+			Step:    "ffmpeg",
+			Message: "Installing yt-dlp via Homebrew...",
+			Percent: 80,
+		})
+		cmd := exec.Command("brew", "install", "yt-dlp")
+		if out, err := cmd.CombinedOutput(); err != nil {
+			// Non-fatal: yt-dlp is optional
+			_ = out
+		}
+	}
+
+	return nil
+}
+
 func removeAutoRestart() {
 	home, err := os.UserHomeDir()
 	if err != nil {

edge-ai-platform/installer/platform_linux.go

@@ -109,6 +109,38 @@ func installAutoRestart(installDir string) error {
 	return nil
 }
 
+func installFfmpeg(inst *Installer, needFfmpeg, needYtdlp bool) error {
+	if _, err := exec.LookPath("apt-get"); err != nil {
+		return fmt.Errorf("package manager not found — please install ffmpeg manually")
+	}
+
+	if needFfmpeg {
+		inst.emitProgress(ProgressEvent{
+			Step:    "ffmpeg",
+			Message: "Installing ffmpeg via apt-get...",
+			Percent: 79,
+		})
+		cmd := exec.Command("pkexec", "apt-get", "install", "-y", "ffmpeg")
+		if out, err := cmd.CombinedOutput(); err != nil {
+			return fmt.Errorf("apt install ffmpeg failed: %s — %w", string(out), err)
+		}
+	}
+
+	if needYtdlp {
+		inst.emitProgress(ProgressEvent{
+			Step:    "ffmpeg",
+			Message: "Installing yt-dlp via pip...",
+			Percent: 80,
+		})
+		cmd := exec.Command("pip3", "install", "yt-dlp")
+		if out, err := cmd.CombinedOutput(); err != nil {
+			_ = out // Non-fatal
+		}
+	}
+
+	return nil
+}
+
 func removeAutoRestart() {
 	exec.Command("systemctl", "--user", "disable", "--now", systemdServiceName+".service").Run()
 

edge-ai-platform/installer/platform_windows.go

@@ -155,6 +155,53 @@ func installAutoRestart(installDir string) error {
 	return nil
 }
 
+func installFfmpeg(inst *Installer, needFfmpeg, needYtdlp bool) error {
+	if _, err := exec.LookPath("winget"); err != nil {
+		return fmt.Errorf("winget not found — please install ffmpeg manually from https://ffmpeg.org")
+	}
+
+	if needFfmpeg {
+		inst.emitProgress(ProgressEvent{
+			Step:    "ffmpeg",
+			Message: "Installing ffmpeg via winget...",
+			Percent: 79,
+		})
+		cmd := exec.Command("winget", "install", "Gyan.FFmpeg",
+			"--accept-source-agreements", "--accept-package-agreements", "--silent")
+		if out, err := cmd.CombinedOutput(); err != nil {
+			return fmt.Errorf("winget install ffmpeg failed: %s — %w", string(out), err)
+		}
+
+		// winget installs ffmpeg to a PATH that requires shell restart.
+		// Add common install location to current process PATH so subsequent checks work.
+		for _, dir := range []string{
+			filepath.Join(os.Getenv("LOCALAPPDATA"), "Microsoft", "WinGet", "Links"),
+			`C:\ffmpeg\bin`,
+			filepath.Join(os.Getenv("ProgramFiles"), "FFmpeg", "bin"),
+		} {
+			if _, err := os.Stat(dir); err == nil {
+				os.Setenv("PATH", dir+";"+os.Getenv("PATH"))
+			}
+		}
+	}
+
+	if needYtdlp {
+		inst.emitProgress(ProgressEvent{
+			Step:    "ffmpeg",
+			Message: "Installing yt-dlp via winget...",
+			Percent: 80,
+		})
+		cmd := exec.Command("winget", "install", "yt-dlp.yt-dlp",
+			"--accept-source-agreements", "--accept-package-agreements", "--silent")
+		if out, err := cmd.CombinedOutput(); err != nil {
+			// Non-fatal: yt-dlp is optional
+			_ = out
+		}
+	}
+
+	return nil
+}
+
 func removeAutoRestart() {
 	// Remove Registry Run key
 	exec.Command("reg", "delete",