Add --version flag and enforce --long flags via pflag

Switches CLI flag parsing from Go's stdlib `flag` to spf13/pflag so
`--project` (and the internal `--socket` / `--identity` / `--scenario`
flags) are the only accepted form; single-hyphen long flags like
`-project` are now rejected. Help output renders the canonical `--`
form.

Adds `patterm --version`, which prints the build version, short commit,
and build date (e.g. `patterm v0.0.1 (commit abc1234, built 2026-05-14)`).
The version string is injected at build time — `make patterm` derives it
from `git describe --tags --always --dirty`, and the release workflow
injects the pushed tag. Commit/date come from the Go toolchain's
embedded VCS info via `runtime/debug.ReadBuildInfo`, so no manual
bumping is required.

cmd/patterm/debug_harness.go

@@ -2,10 +2,11 @@ package main
 
 import (
 	"encoding/json"
-	"flag"
 	"fmt"
 	"os"
 
+	flag "github.com/spf13/pflag"
+
 	"github.com/hjbdev/patterm/internal/harness"
 )
 

cmd/patterm/main.go

@@ -4,6 +4,7 @@
 //
 //	patterm                      run in $PWD
 //	patterm --project <dir>      run in <dir>
+//	patterm --version            print version and exit
 //	patterm mcp-stdio --socket S --identity I
 //	                             internal: stdio MCP proxy spawned for
 //	                             children, forwards JSON-RPC over S
@@ -13,15 +14,22 @@ package main
 
 import (
 	"context"
-	"flag"
 	"fmt"
 	"os"
+	"runtime/debug"
+	"time"
+
+	flag "github.com/spf13/pflag"
 
 	"github.com/hjbdev/patterm/internal/app"
 	"github.com/hjbdev/patterm/internal/mcp"
 	"github.com/hjbdev/patterm/internal/projectkey"
 )
 
+// version is overridden at build time via `-ldflags "-X main.version=..."`.
+// Defaults to "dev" so source builds are still meaningful.
+var version = "dev"
+
 func main() {
 	// The mcp-stdio subcommand is a separate top-level mode: when an
 	// agent CLI launches `patterm mcp-stdio --socket ...`, the same
@@ -38,9 +46,17 @@ func main() {
 		return
 	}
 
-	var projectDir = flag.String("project", "", "project directory (default $PWD)")
+	var (
+		projectDir  = flag.String("project", "", "project directory (default $PWD)")
+		showVersion = flag.Bool("version", false, "print version and exit")
+	)
 	flag.Parse()
 
+	if *showVersion {
+		fmt.Println(versionString())
+		return
+	}
+
 	cwd, err := os.Getwd()
 	if err != nil {
 		die("getwd: %v", err)
@@ -80,6 +96,33 @@ func runMCPProxy() {
 	}
 }
 
+func versionString() string {
+	commit, date := "unknown", "unknown"
+	if info, ok := debug.ReadBuildInfo(); ok {
+		dirty := false
+		for _, s := range info.Settings {
+			switch s.Key {
+			case "vcs.revision":
+				if len(s.Value) >= 7 {
+					commit = s.Value[:7]
+				} else if s.Value != "" {
+					commit = s.Value
+				}
+			case "vcs.time":
+				if t, err := time.Parse(time.RFC3339, s.Value); err == nil {
+					date = t.Format("2006-01-02")
+				}
+			case "vcs.modified":
+				dirty = s.Value == "true"
+			}
+		}
+		if dirty && commit != "unknown" {
+			commit += "-dirty"
+		}
+	}
+	return fmt.Sprintf("patterm %s (commit %s, built %s)", version, commit, date)
+}
+
 func die(format string, args ...any) {
 	fmt.Fprintf(os.Stderr, "patterm: "+format+"\n", args...)
 	os.Exit(1)