feat(gradle): release v1.6.0 — Gradle build file version bump

Add internal/gradle package with ReadVersion and WriteVersion for
build.gradle (Groovy DSL, single-quoted) and build.gradle.kts (Kotlin
DSL, double-quoted). Quote style is preserved on write. regexp.QuoteMeta
ensures version strings with dots or special characters are safe.

Config follows the established multi-value pattern:
- gradle.build_file: single path (opt-in, no default)
- gradle.build_files: list for multi-module projects (overrides build_file)
- --gradle flag overrides build_file and clears build_files

100% per-package statement coverage maintained across all 13 packages;
FuzzReadVersion and FuzzWriteVersion added per fuzzing guidelines.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

internal/gradle/gradle.go

@@ -0,0 +1,54 @@
+package gradle
+
+import (
+	"fmt"
+	"os"
+	"regexp"
+)
+
+// versionRe matches a Gradle/Kotlin DSL version assignment on its own line.
+// Group 1 captures the version string (without quotes).
+// Handles both double-quoted (Kotlin/Groovy) and single-quoted (Groovy) forms,
+// with or without spaces around =.
+var versionRe = regexp.MustCompile(`(?m)^[ \t]*version\s*=\s*["']([^"']+)["']`)
+
+// ReadVersion returns the version value from a build.gradle or build.gradle.kts file.
+func ReadVersion(path string) (string, error) {
+	data, err := os.ReadFile(path)
+	if err != nil {
+		return "", fmt.Errorf("read %s: %w", path, err)
+	}
+	m := versionRe.FindStringSubmatch(string(data))
+	if m == nil {
+		return "", fmt.Errorf("no version assignment found in %s", path)
+	}
+	return m[1], nil
+}
+
+// WriteVersion replaces the version assignment in a build.gradle or build.gradle.kts
+// file in-place. oldVersion must match what ReadVersion returned. Quote style is preserved.
+func WriteVersion(path, oldVersion, newVersion string) error {
+	data, err := os.ReadFile(path)
+	if err != nil {
+		return fmt.Errorf("read %s: %w", path, err)
+	}
+	updated, ok := replaceVersion(string(data), oldVersion, newVersion)
+	if !ok {
+		return fmt.Errorf("version %q not found in %s", oldVersion, path)
+	}
+	return os.WriteFile(path, []byte(updated), 0644)
+}
+
+// replaceVersion finds and replaces the first version assignment line in a Gradle build file.
+// Quote style (single or double) of the original line is preserved.
+// Returns the updated content and true if a replacement was made.
+func replaceVersion(content, oldVersion, newVersion string) (string, bool) {
+	re := regexp.MustCompile(`(?m)^([ \t]*version\s*=\s*)(["'])` + regexp.QuoteMeta(oldVersion) + `["']`)
+	m := re.FindStringSubmatchIndex(content)
+	if m == nil {
+		return content, false
+	}
+	prefix := content[m[2]:m[3]] // "version = " etc., preserving whitespace
+	quote := content[m[4]:m[5]]  // " or '
+	return content[:m[0]] + prefix + quote + newVersion + quote + content[m[1]:], true
+}