chore(env): remove deprecated .env.custom and add 90-project.env

Author: mrz1836

.github/.env.custom

@@ -0,0 +1,31 @@
+# ================================================================================================
+# 🏗️ PROJECT-SPECIFIC CONFIGURATION (90-project.env)
+# ================================================================================================
+#
+# Purpose: Project-specific overrides that are NOT synced to other repos via go-broadcast
+# Load Order: 90 (loaded after all default/tool configs, overrides everything before it)
+#
+# This file contains settings unique to this repository:
+# - Coverage provider and reporting overrides
+# - Coverage path exclusions (aligned with codecov.yml)
+#
+# This file is NOT synced via go-broadcast. Edit freely for this project's needs.
+#
+# ================================================================================================
+
+# ================================================================================================
+# 📊 COVERAGE PROVIDER OVERRIDES
+# ================================================================================================
+
+# Use Codecov as the coverage provider (overrides default: internal)
+GO_COVERAGE_PROVIDER=codecov
+
+# Require Codecov token for uploads
+CODECOV_TOKEN_REQUIRED=true
+
+# ================================================================================================
+# 🚫 COVERAGE EXCLUSIONS (aligned with codecov.yml)
+# ================================================================================================
+
+# Exclude paths from coverage reporting (matches codecov.yml ignore list)
+GO_COVERAGE_EXCLUDE_PATHS=.github/,.mage-cache/,.vscode/,bin/,example/,examples/,mocks/,test/,testing/,vendor/,testdata/