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/llm.py

@@ -7,7 +7,7 @@ from contextlib import asynccontextmanager
 
 import litellm
 from app.core.config import DEFAULT_MODEL, DEBUG
-from app.core.websearch import WEB_SEARCH_TOOL, search_web
+from app.core.search.websearch import WEB_SEARCH_TOOL, search_web
 
 litellm.drop_params = True
 if DEBUG:
@@ -97,6 +97,12 @@ async def complete(
     return result
 
 
+async def embed(texts: list[str], model: str) -> list[list[float]]:
+    """テキスト群を埋め込みベクトルに変換する。"""
+    response = await litellm.aembedding(model=model, input=texts)
+    return [item["embedding"] for item in response.data]
+
+
 async def resolve_web_search(
     messages: list[dict],
     model: str | None = None,