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.

go.mod

@@ -4,6 +4,7 @@ go 1.26.3
 
 require (
 	github.com/creack/pty v1.1.24
+	github.com/spf13/pflag v1.0.10
 	golang.org/x/term v0.43.0
 )