feat: test go 1.18 and mage-x

Author: mrz1836

.github/.env.base

@@ -30,7 +30,7 @@ GO_PRIMARY_VERSION=1.24.x
 
 # Secondary Go version for compatibility testing
 # Set to same as primary to test with single version only
-GO_SECONDARY_VERSION=1.24.x
+GO_SECONDARY_VERSION=1.18.x
 
 # ================================================================================================
 # 🖥️ RUNNER CONFIGURATION

.github/.env.shared

@@ -19,7 +19,6 @@ This repository uses **`AGENTS.md`** as the single source of truth for:
 2. **Follow branch‑prefix and commit‑message standards**
    They drive Mergify auto‑labeling and CI gates.
 3. **Never tag releases**
-   Only repository code‑owners run `make tag` / `make release`.
 4. **Pass CI**
    Run `go fmt`, `goimports`, `go vet`, `staticcheck`, and `golangci‑lint` locally before opening a PR.
 

.github/CLAUDE.md

@@ -179,6 +179,19 @@ extra baggage.
 
 ### Additional Documentation & Repository Management
 
+<details>
+<summary><strong><code>Development Setup (Getting Started)</code></strong></summary>
+<br/>
+
+Install [MAGE-X](https://github.com/mrz1836/mage-x) build tool for development:
+
+```bash
+# Install MAGE-X for development and building
+go install github.com/mrz1836/mage-x/cmd/magex@latest
+magex update:install
+```
+</details>
+
 <details>
 <summary><strong><code>Library Deployment</code></strong></summary>
 <br/>