chore(env): migrate custom configuration to project-specific env file

Author: mrz1836

.github/.env.custom

@@ -0,0 +1,27 @@
+# ================================================================================================
+# 🏗️ PROJECT-SPECIFIC CONFIGURATION (90-project.env)
+# ================================================================================================
+#
+# Purpose: Project-specific overrides for go-lockfree-queue
+# Load Order: 90 (project overrides, loaded last to override all defaults)
+#
+# This file contains project-specific configuration that overrides defaults
+# from lower-numbered env files. Settings here take highest priority.
+#
+# ================================================================================================
+
+# ================================================================================================
+# 📊 COVERAGE CONFIGURATION
+# ================================================================================================
+
+# Coverage Provider (override: use codecov instead of internal)
+GO_COVERAGE_PROVIDER=codecov
+
+# Codecov Configuration
+CODECOV_TOKEN_REQUIRED=true
+
+# Coverage Exclusions (matches codecov.yml ignore paths)
+GO_COVERAGE_EXCLUDE_PATHS=.github/,.mage-cache/,.vscode/,bin/,example/,examples/,mocks/,testing/,test/,vendor/,testdata/,plans/,docs/
+
+# Skip URL Checks in Coverage Reports
+GO_COVERAGE_SKIP_URL_CHECKS=true