DEVX-141: feat: add promtool to install_tools for alert rule validation

src/devx/tools/install_tools.py

@@ -8,6 +8,7 @@ Handles installation of:
 - tea (Gitea CLI — official command-line tool for Gitea API operations)
 - hadolint (Dockerfile linter)
 - vale (prose linter for documentation quality)
+- promtool (Prometheus rule validator)
 
 Each tool is installed to ``~/.local/bin`` if not already on PATH.
 Idempotent: skips tools that are already available.
@@ -47,6 +48,8 @@ TOFU_VERSION = "1.12.3"
 
 VALE_VERSION = "3.15.1"
 
+PROMTOOL_VERSION = "3.5.5"
+
 
 def _arch() -> str:
     """Return the architecture string used by release assets (delegates to shared utility)."""
@@ -212,7 +215,26 @@ def install_vale() -> bool:
     return True
 
 
-TOOL_NAMES = ["actionlint", "git-cliff", "act_runner", "tea", "hadolint", "tofu", "vale"]
+def install_promtool() -> bool:
+    """Install promtool (Prometheus rule validator) if not already present.
+
+    Downloads the official Prometheus release tarball from GitHub and
+    extracts the ``promtool`` binary to ``~/.local/bin``.
+    """
+    if _is_installed("promtool"):
+        click.echo("promtool: already installed")
+        return True
+    arch = _arch()
+    url = (
+        f"https://github.com/prometheus/prometheus/releases/download/"
+        f"v{PROMTOOL_VERSION}/prometheus-{PROMTOOL_VERSION}.linux-{arch}.tar.gz"
+    )
+    dest = _download_and_extract_tarball(url, "promtool")
+    click.echo(f"promtool: installed to {dest}")
+    return True
+
+
+TOOL_NAMES = ["actionlint", "git-cliff", "act_runner", "tea", "hadolint", "tofu", "vale", "promtool"]
 
 
 def _install_tool(name: str) -> bool:
@@ -231,6 +253,8 @@ def _install_tool(name: str) -> bool:
         return install_tofu()
     if name == "vale":
         return install_vale()
+    if name == "promtool":
+        return install_promtool()
     raise click.ClickException(f"Unknown tool: {name}")