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.

.gitea/workflows/release.yml

@@ -30,7 +30,8 @@ jobs:
           CGO_ENABLED: 1
         run: |
           mkdir -p dist
-          go build -trimpath -ldflags="-s -w" \
+          go build -trimpath \
+            -ldflags="-s -w -X main.version=${{ github.ref_name }}" \
             -o dist/patterm-${{ github.ref_name }}-linux-amd64 \
             ./cmd/patterm