feat: add GitHub repository dashboard with Prometheus metrics

ghtracker authenticates as a GitHub App and scans a configured list of repositories on a schedule. It serves a dashboard, a JSON state endpoint, a health probe and Prometheus metrics.

The dashboard lists only items that need attention: failing workflows, pull requests that wait too long or fail their checks, stale issues and projects that failed to scan. It has search, dynamic filters and a button that rescans on demand. The Vue app is embedded in the Go binary.

The client protects the GitHub rate limit with conditional requests, a request reserve and Retry-After handling.

workflow-prepare.sh

@@ -0,0 +1,34 @@
+#!/usr/bin/env bash
+# Run by the shared release workflow before the tests, the version calculation and
+# GoReleaser. The binary embeds dist/, so the UI must be built first.
+set -euo pipefail
+
+PNPM_VERSION=11.21.0 # keep in sync with packageManager in package.json
+NODE_VERSION=22.23.3
+NODE_SHA256_LINUX_X64=df450af89261115ef9f9e3830c3eeb2cc9213b63c720b1af623cb5dcbe2e02de
+NODE_MIN="22.13.0" # pnpm 11 needs Node 22.13 or newer
+
+node_ok() {
+  command -v node >/dev/null 2>&1 &&
+    [ "$(printf '%s\n%s\n' "$NODE_MIN" "$(node -p 'process.versions.node')" | sort -V | head -n1)" = "$NODE_MIN" ]
+}
+
+install_node() {
+  if [ "$(uname -s)-$(uname -m)" != "Linux-x86_64" ]; then
+    echo "Node >= $NODE_MIN is required; install it and run again." >&2
+    exit 1
+  fi
+  local dir="${RUNNER_TEMP:-/tmp}/node-v${NODE_VERSION}"
+  local archive="node-v${NODE_VERSION}-linux-x64.tar.xz"
+  mkdir -p "$dir"
+  curl -fsSL "https://nodejs.org/dist/v${NODE_VERSION}/${archive}" -o "$dir/$archive"
+  echo "${NODE_SHA256_LINUX_X64}  $dir/$archive" | sha256sum -c -
+  tar -xJf "$dir/$archive" -C "$dir" --strip-components=1
+  export PATH="$dir/bin:$PATH"
+  if [ -n "${GITHUB_PATH:-}" ]; then echo "$dir/bin" >> "$GITHUB_PATH"; fi
+}
+
+node_ok || install_node
+
+npx --yes "pnpm@${PNPM_VERSION}" install --frozen-lockfile
+npx --yes "pnpm@${PNPM_VERSION}" build