feat: add lint, build, test, push pipeline with SHA-pinned actions

- Split single build job into 4 jobs: lint, build, test, push
- SHA-pin all actions for supply chain security
- Use ChristopherHX artifact actions (Gitea-compatible)
- Switch to root build context (Dockerfile does COPY ../public)
- Add tests/test.sh with Docker bridge gateway networking

tests/test.sh

@@ -0,0 +1,55 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+IMAGE="${1:?Usage: test.sh <image>}"
+CONTAINER_NAME="test-$(echo "$IMAGE" | tr ':/' '-')-$$"
+PASSED=0
+FAILED=0
+TOTAL=0
+
+cleanup() {
+  docker rm -f "$CONTAINER_NAME" >/dev/null 2>&1 || true
+}
+trap cleanup EXIT
+
+assert() {
+  local name="$1" expected="$2" actual="$3"
+  TOTAL=$((TOTAL + 1))
+  if [ "$expected" = "$actual" ]; then
+    echo "  PASS: $name"
+    PASSED=$((PASSED + 1))
+  else
+    echo "  FAIL: $name (expected: '$expected', got: '$actual')"
+    FAILED=$((FAILED + 1))
+  fi
+}
+
+echo "Running container: $IMAGE"
+docker run -d --name "$CONTAINER_NAME" -p 8080:80 "$IMAGE" >/dev/null
+
+DOCKER_GW=$(docker network inspect bridge --format '{{range .IPAM.Config}}{{.Gateway}}{{end}}')
+BASE_URL="http://${DOCKER_GW}:8080"
+
+echo "Waiting for container on ${DOCKER_GW}:8080..."
+for i in $(seq 1 30); do
+  if [ "$(curl -s -o /dev/null -w '%{http_code}' "$BASE_URL/" 2>/dev/null)" != "000" ]; then
+    echo "Container ready after ${i}s"
+    break
+  fi
+  if [ "$i" -eq 30 ]; then
+    echo "FAIL: Container did not become ready within 30s"
+    docker logs "$CONTAINER_NAME"
+    exit 1
+  fi
+  sleep 1
+done
+
+echo ""
+echo "Test: GET / (basic_auth should return 401)"
+STATUS=$(curl -s -o /dev/null -w '%{http_code}' "$BASE_URL/")
+
+assert "HTTP status is 401 (Unauthorized)" "401" "$STATUS"
+
+echo ""
+echo "Results: $PASSED/$TOTAL passed, $FAILED failed"
+[ "$FAILED" -eq 0 ]