Add Reddit monitoring bot — backend, frontend, and Docker config

Python/FastAPI backend with PostgreSQL for collecting Reddit data via
public .json endpoints. React/Vite dashboard for analytics. Docker Compose
setup with API and worker services connecting to shared PostgreSQL.

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

backend/worker/reddit_client.py

@@ -0,0 +1,58 @@
+import asyncio
+import logging
+import time
+
+import httpx
+
+from backend.config import settings
+
+logger = logging.getLogger(__name__)
+
+BASE_URL = "https://www.reddit.com"
+
+# Simple in-process rate limiter: track request timestamps
+_request_times: list[float] = []
+MAX_REQUESTS_PER_MINUTE = 9  # Stay under Reddit's ~10/min limit
+
+
+async def _wait_for_rate_limit():
+    """Block until we have budget for another request."""
+    now = time.monotonic()
+    # Remove timestamps older than 60 seconds
+    while _request_times and _request_times[0] < now - 60:
+        _request_times.pop(0)
+    if len(_request_times) >= MAX_REQUESTS_PER_MINUTE:
+        wait = 60 - (now - _request_times[0]) + 0.5
+        logger.info(f"Rate limit: waiting {wait:.1f}s")
+        await asyncio.sleep(wait)
+    _request_times.append(time.monotonic())
+
+
+async def fetch_json(client: httpx.AsyncClient, path: str, params: dict | None = None) -> dict | None:
+    """Fetch a Reddit .json endpoint with rate limiting and error handling."""
+    await _wait_for_rate_limit()
+    url = f"{BASE_URL}{path}.json"
+    try:
+        response = await client.get(url, params=params)
+        if response.status_code == 429:
+            retry_after = int(response.headers.get("Retry-After", 60))
+            logger.warning(f"Rate limited, waiting {retry_after}s")
+            await asyncio.sleep(retry_after)
+            return await fetch_json(client, path, params)
+        if response.status_code >= 500:
+            logger.warning(f"Reddit returned {response.status_code} for {path}")
+            return None
+        response.raise_for_status()
+        return response.json()
+    except httpx.HTTPError as e:
+        logger.error(f"HTTP error fetching {path}: {e}")
+        return None
+
+
+def create_client() -> httpx.AsyncClient:
+    """Create an httpx client configured for Reddit."""
+    return httpx.AsyncClient(
+        headers={"User-Agent": settings.reddit_user_agent},
+        timeout=30.0,
+        follow_redirects=True,
+    )