feat: add --version flag to root command (#15)

* feat: add --version flag to root command

Why: Users expect --version flag as standard CLI pattern (issue #9)
Approach: Set rootCmd.Version in createRootCmd, add functional tests
Learned: Cobra auto-adds -v/--version when Version field is set
Next: Create PR and close issue

Changes:
- Added rootCmd.Version = config.Version in createRootCmd()
- Added functional tests for both 'version' subcommand and '--version' flag
- Tests verify output format and exit code
- All tests pass

Fixes #9

🤖 Claude <[email protected]>

* test: add proper version output validation with CheckFuncs

Why: Need to validate version output format supports both 'unknown' and version strings
Approach: Use CheckFuncs to validate output format while stripping variable content
Learned: CheckFunc provides better validation than regex for variable content
Next: Push and verify CI passes

Changes:
- Added strings import to data_for_test.go
- Added CheckFunc for version subcommand to validate format
- Added CheckFunc for --version flag to validate 'otel-cli version X' format
- Both CheckFuncs handle 'unknown' or multi-part version strings
- Use regex  to strip content for checkOutput comparison

🤖 Claude <[email protected]>

Author: tobert

data_for_test.go

@@ -10,6 +10,7 @@ package main_test
 import (
 	"os"
 	"regexp"
+	"strings"
 	"syscall"
 	"testing"
 	"time"
@@ -1373,4 +1374,64 @@ var suites = []FixtureSuite{
 			},
 		},
 	},
+	// version flag tests
+	{
+		{
+			Name: "version subcommand",
+			Config: FixtureConfig{
+				CliArgs: []string{"version"},
+			},
+			Expect: Results{
+				CliOutputRe: regexp.MustCompile(`.+`), // match and strip any content
+				CliOutput:   "\n",                      // after strip, should be just newline
+				ExitCode:    0,
+			},
+			CheckFuncs: []CheckFunc{
+				func(t *testing.T, f Fixture, r Results) {
+					// version subcommand outputs just the version string
+					// should be "unknown" or "version commit date"
+					output := strings.TrimSpace(r.CliOutput)
+					if output == "" {
+						t.Errorf("version subcommand produced no output")
+						return
+					}
+					// valid outputs: "unknown" or multi-part version like "0.6.0 abc123 2025-11-09"
+					if output != "unknown" && !regexp.MustCompile(`^\S+`).MatchString(output) {
+						t.Errorf("version subcommand output format unexpected: %q", output)
+					}
+				},
+			},
+		},
+		{
+			Name: "--version flag",
+			Config: FixtureConfig{
+				CliArgs: []string{"--version"},
+			},
+			Expect: Results{
+				CliOutputRe: regexp.MustCompile(`.+`), // match and strip any content
+				CliOutput:   "\n",                      // after strip, should be just newline
+				ExitCode:    0,
+			},
+			CheckFuncs: []CheckFunc{
+				func(t *testing.T, f Fixture, r Results) {
+					// --version flag outputs "otel-cli version <version>"
+					output := strings.TrimSpace(r.CliOutput)
+					if !strings.HasPrefix(output, "otel-cli version ") {
+						t.Errorf("--version flag should start with 'otel-cli version ', got: %q", output)
+						return
+					}
+					// extract version part after "otel-cli version "
+					version := strings.TrimPrefix(output, "otel-cli version ")
+					if version == "" {
+						t.Errorf("--version flag has no version content after prefix")
+						return
+					}
+					// valid version: "unknown" or multi-part like "0.6.0 abc123 2025-11-09"
+					if version != "unknown" && !regexp.MustCompile(`^\S+`).MatchString(version) {
+						t.Errorf("--version flag version format unexpected: %q", version)
+					}
+				},
+			},
+		},
+	},
 }

otelcli/root.go

@@ -59,6 +59,7 @@ func createRootCmd(config *Config) *cobra.Command {
 
 	cobra.EnableCommandSorting = false
 	rootCmd.Flags().SortFlags = false
+	rootCmd.Version = config.Version
 
 	Diag.NumArgs = len(os.Args) - 1
 	Diag.CliArgs = []string{}