fix(build): sync APP_VERSION to 3.1.3 and prefer git tag for version

APP_VERSION was stuck at 3.0.0 because the auto-generated update PRs
for 3.x releases (created by pre_release.yml) were being closed without
merging. GoReleaser-built release binaries correctly embed the version
from the git tag, but local builds via `make build` were reporting
3.0.0 instead of 3.1.3.

Two changes:
- Update APP_VERSION to 3.1.3 (current latest release)
- Make getVersion() try an exact git tag on HEAD before falling back to
  APP_VERSION, matching GoReleaser's {{.Version}} behavior. This means
  local builds on any tagged commit will always report the correct
  release version independently of the APP_VERSION file.

Co-Authored-By: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>

Author: jlec

APP_VERSION

@@ -1 +1 @@
-3.0.0
+3.1.3

scripts/build-tool/main.go

@@ -357,6 +357,13 @@ Examples:
 
 // Helper functions
 func getVersion() string {
+	// Prefer an exact git tag on HEAD — matches goreleaser's {{.Version}} behavior
+	// so `make build` on a tagged commit always reports the correct release version.
+	if output, err := utils.RunCommandOutput("git", "describe", "--tags", "--exact-match", "HEAD"); err == nil {
+		if v := strings.TrimSpace(strings.TrimPrefix(output, "v")); v != "" {
+			return v
+		}
+	}
 	if content, err := os.ReadFile("APP_VERSION"); err == nil {
 		return strings.TrimSpace(string(content))
 	}