refactor: deduplicate shared code into shared/ module

Move duplicated files from chat + batch-agent into shared/:
- shared/ws_context.py — Redis-based tool call round-trip
- shared/llm.py — LiteLLM factory (get_llm, embed)
- shared/agents/ — 4 domain agents (task, note, project, timeline)

Update all service imports to use shared.* instead of app.*.
Delete 12 duplicated files across both services.

services/batch-agent/app/llm.py

@@ -1,78 +0,0 @@
-"""LLM factory — centralised model instantiation via LiteLLM.
-
-Identical to services/chat/app/llm.py. Uses shared.config.settings.
-"""
-
-from __future__ import annotations
-
-import os
-import warnings
-
-from openai import AsyncOpenAI
-import litellm
-
-from langchain_openai import ChatOpenAI
-from langchain_litellm import ChatLiteLLM
-
-from shared.config import settings
-
-litellm.drop_params = True
-
-warnings.filterwarnings(
-    "ignore",
-    message=r"PydanticSerializationUnexpectedValue\(Expected `ResponseAPIUsage`",
-    category=UserWarning,
-)
-
-
-def _api_key_for_model(model: str) -> str | None:
-    if model.startswith("anthropic/"):
-        return settings.ANTHROPIC_API_KEY or None
-    if model.startswith("gemini/") or model.startswith("google/"):
-        return settings.GOOGLE_API_KEY or None
-    if model.startswith("cerebras/"):
-        return settings.CEREBRAS_API_KEY or None
-    if model.startswith("github_copilot/"):
-        return None
-    return settings.OPENAI_API_KEY or None
-
-
-def get_llm(
-    *,
-    model: str | None = None,
-    temperature: float = 0,
-    callbacks: list | None = None,
-) -> ChatOpenAI | ChatLiteLLM:
-    model = model or settings.LLM_MODEL
-
-    if settings.GITHUB_COPILOT_TOKEN_DIR:
-        os.environ.setdefault("GITHUB_COPILOT_TOKEN_DIR", settings.GITHUB_COPILOT_TOKEN_DIR)
-
-    if "/" in model:
-        return ChatLiteLLM(model=model, temperature=temperature, callbacks=callbacks)
-
-    return ChatOpenAI(
-        model=model,
-        temperature=temperature,
-        api_key=_api_key_for_model(model),
-        callbacks=callbacks,
-    )
-
-
-def get_router_llm(
-    *,
-    temperature: float = 0,
-) -> ChatOpenAI | ChatLiteLLM:
-    return get_llm(model=settings.LLM_ROUTER_MODEL, temperature=temperature)
-
-
-async def embed(text: str) -> list[float]:
-    model = settings.LLM_EMBED_MODEL
-
-    if model.startswith("github_copilot/") or "/" in model:
-        response = await litellm.aembedding(model=model, input=[text])
-        return response.data[0]["embedding"]
-
-    client = AsyncOpenAI(api_key=settings.OPENAI_API_KEY)
-    response = await client.embeddings.create(model=model, input=text)
-    return response.data[0].embedding