fix: resolve mypy errors, fix arxiv test session isolation, and add premerge script

- Remove unused type:ignore comment in scholars.py
- Fix 51 mypy errors across test files (Any return types, cast(), protocol stubs)
- Fix arxiv unit test failures caused by session isolation (patch_session_factory fixture)
- Fix integration test rate-limit bleed between search and create
- Add scripts/premerge.sh for local CI verification
- Add docs/website/.docusaurus/ to .gitignore

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

scripts/premerge.sh

@@ -0,0 +1,58 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+DC="docker compose -f docker-compose.yml -f docker-compose.dev.yml"
+
+passed=0
+failed=0
+failures=()
+
+step() {
+  local label="$1"
+  shift
+  printf '\n\033[1;34m── %s\033[0m\n' "$label"
+  if "$@"; then
+    printf '\033[1;32m   PASS\033[0m  %s\n' "$label"
+    ((passed++)) || true
+  else
+    printf '\033[1;31m   FAIL\033[0m  %s\n' "$label"
+    ((failed++)) || true
+    failures+=("$label")
+  fi
+}
+
+# ── repo hygiene (host-side, no runtime deps) ────────────────────────────────
+step "No generated artifacts"        ./scripts/check_no_generated_artifacts.sh
+step "Env contract parity"           python3 scripts/check_env_contract.py
+step "API contract drift"            python3 scripts/check_frontend_api_contract.py
+
+# ── backend lint + typecheck ─────────────────────────────────────────────────
+step "Ruff check"                    $DC run --rm app ruff check .
+step "Ruff format"                   $DC run --rm app ruff format --check .
+step "Mypy"                          $DC run --rm app mypy app/ --ignore-missing-imports
+
+# ── backend tests ────────────────────────────────────────────────────────────
+step "Unit tests"                    $DC run --rm app python -m pytest tests/unit
+step "Integration tests"             $DC run --rm app python -m pytest -m integration
+
+# ── frontend ─────────────────────────────────────────────────────────────────
+step "Frontend theme tokens"         $DC run --rm frontend npm run check:theme-tokens
+step "Frontend typecheck"            $DC run --rm frontend npm run typecheck
+step "Frontend unit tests"           $DC run --rm frontend npm run test:run
+step "Frontend build"                $DC run --rm frontend npm run build
+
+# ── docs ─────────────────────────────────────────────────────────────────────
+step "Docs build"                    npm --prefix docs/website run build
+
+# ── summary ──────────────────────────────────────────────────────────────────
+printf '\n\033[1;34m── Summary ─────────────────────────────────────────────\033[0m\n'
+printf '   %s passed, %s failed\n' "$passed" "$failed"
+if ((failed > 0)); then
+  printf '\n\033[1;31m   Failed steps:\033[0m\n'
+  for f in "${failures[@]}"; do
+    printf '     - %s\n' "$f"
+  done
+  exit 1
+else
+  printf '\n\033[1;32m   All checks passed.\033[0m\n'
+fi