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.

CHANGELOG.md

@@ -6,6 +6,21 @@ loosely follows [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
 
+### Added
+- `patterm --version` prints the build version, git commit, and build
+  date (e.g. `patterm v0.0.1 (commit abc1234, built 2026-05-14)`). The
+  version string is injected by the build (`make patterm` derives it
+  from `git describe`; the release workflow injects the pushed tag).
+  Commit and date come from the Go toolchain's embedded VCS info, so
+  nothing has to be bumped by hand.
+
+### Changed
+- CLI flag parsing switched from Go's stdlib `flag` to `spf13/pflag`.
+  `--project` (and the internal `--socket` / `--identity` /
+  `--scenario` / `--patterm-bin` flags) are now the only accepted form
+  — single-hyphen long flags like `-project` are rejected. Help output
+  renders the canonical `--flag` form.
+
 ## [0.0.1] - 2026-05-14
 
 ### Fixed