feat: add CLI wrapper script for the reddit-post sidecar

Implements run.sh with argument parsing (--username, --password, --subreddit,
--title, --body, optional --headed), environment variable mapping to Task 2's
env contract, Playwright invocation with proper exit-code capture via set +e,
and result file output to stdout.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

sidecars/reddit-post/run.sh

@@ -0,0 +1,63 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+cd "$SCRIPT_DIR"
+
+USERNAME=""
+PASSWORD=""
+SUBREDDIT=""
+TITLE=""
+BODY=""
+HEADLESS_FLAG="true"
+
+for arg in "$@"; do
+  case "$arg" in
+    --username=*) USERNAME="${arg#*=}" ;;
+    --password=*) PASSWORD="${arg#*=}" ;;
+    --subreddit=*) SUBREDDIT="${arg#*=}" ;;
+    --title=*) TITLE="${arg#*=}" ;;
+    --body=*) BODY="${arg#*=}" ;;
+    --headed) HEADLESS_FLAG="false" ;;
+    *)
+      echo "{\"success\": false, \"error\": \"Unknown argument: $arg\"}"
+      exit 1
+      ;;
+  esac
+done
+
+MISSING=""
+[ -z "$USERNAME" ] && MISSING="$MISSING --username"
+[ -z "$PASSWORD" ] && MISSING="$MISSING --password"
+[ -z "$SUBREDDIT" ] && MISSING="$MISSING --subreddit"
+[ -z "$TITLE" ] && MISSING="$MISSING --title"
+[ -z "$BODY" ] && MISSING="$MISSING --body"
+
+if [ -n "$MISSING" ]; then
+  echo "{\"success\": false, \"error\": \"Missing required argument(s):$MISSING\"}"
+  exit 1
+fi
+
+export REDDIT_USERNAME="$USERNAME"
+export REDDIT_PASSWORD="$PASSWORD"
+export SUBREDDIT="$SUBREDDIT"
+export POST_TITLE="$TITLE"
+export POST_BODY="$BODY"
+export HEADLESS="$HEADLESS_FLAG"
+
+set +e
+npx playwright test tests/reddit-post.spec.js
+PLAYWRIGHT_EXIT_CODE=$?
+set -e
+
+RESULT_FILE="test-results/result.json"
+
+if [ -f "$RESULT_FILE" ]; then
+  cat "$RESULT_FILE"
+  echo
+else
+  echo "{\"success\": false, \"error\": \"Test did not produce a result file\"}"
+  exit 1
+fi
+
+exit "$PLAYWRIGHT_EXIT_CODE"