Reorganize core into subpackages, add local KB, ruff/pyright tooling

- Split backend/app/core into weather/, discord/, memory_kb/, search/
  subpackages by responsibility, keeping config.py and llm.py as the
  shared foundation; updated all import sites accordingly.
- Add local Markdown knowledge base support (local_knowledge.py,
  knowledge_base/fgo.md, LOCAL_KB_* settings) that embeds and injects
  relevant docs into the system prompt by topic similarity.
- Add ruff and pyright as backend dev dependencies with basic config
  in pyproject.toml for linting and type checking.
- Document local machine quirks in CLAUDE.md (Postgres on port 8080,
  SSLKEYLOGFILE breaking litellm/pyright via OPENSSL_Uplink crashes).
- Add backend/run_dev.ps1 dev launcher and docs/discord-bot.md.

backend/app/core/discord/notify.py

@@ -0,0 +1,13 @@
+"""Discord Webhook への通知送信。"""
+import logging
+
+import httpx
+
+logger = logging.getLogger(__name__)
+
+
+async def send_discord_message(webhook_url: str, content: str) -> None:
+    async with httpx.AsyncClient(timeout=10.0) as client:
+        response = await client.post(webhook_url, json={"content": content})
+        response.raise_for_status()
+        logger.info("Discord message sent (status=%s)", response.status_code)