Phase 28: P3 — Pydantic Settings, dependency-injector IoC, tenacity retry

- config.py: dataclasses → pydantic-settings BaseSettings (flat AppConfig,
  env vars auto-loaded from .env, type-safe validation)
- api_client.py: HTTPAPIClient takes AppConfig directly (APIConfig removed);
  tenacity retry on 5 methods (reset/ingest/list/delete/feedback) —
  retries on 5xx + TransportError, 3 attempts, exponential backoff 1-8s
- container.py: manual DI → dependency_injector DeclarativeContainer with
  providers.Singleton; Container() needs no args
- app.py: container.X → container.X() calls, remove AppConfig import
- requirements.txt: add pydantic-settings, tenacity, dependency-injector

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

api_client.py

@@ -5,8 +5,23 @@ import urllib.parse
 from typing import AsyncIterator, Protocol, runtime_checkable
 
 import httpx
+from tenacity import retry, retry_if_exception, stop_after_attempt, wait_exponential
 
-from config import APIConfig
+from config import AppConfig
+
+
+def _is_transient(exc: Exception) -> bool:
+    if isinstance(exc, httpx.HTTPStatusError):
+        return exc.response.status_code >= 500
+    return isinstance(exc, httpx.TransportError)
+
+
+_retry = retry(
+    retry=retry_if_exception(_is_transient),
+    stop=stop_after_attempt(3),
+    wait=wait_exponential(multiplier=1, min=1, max=8),
+    reraise=True,
+)
 
 
 @runtime_checkable
@@ -29,11 +44,12 @@ class APIClientProtocol(Protocol):
 
 
 class HTTPAPIClient:
-    def __init__(self, config: APIConfig):
-        self._url = config.url.rstrip("/")
-        self._timeout = config.timeout
+    def __init__(self, config: AppConfig):
+        self._url = config.youlbot_api_url.rstrip("/")
+        self._timeout = config.youlbot_api_timeout
         self._client = httpx.AsyncClient(
-            headers={"Authorization": f"Bearer {config.token}"} if config.token else {},
+            headers={"Authorization": f"Bearer {config.youlbot_api_token}"}
+            if config.youlbot_api_token else {},
         )
 
     async def chat(
@@ -63,6 +79,7 @@ class HTTPAPIClient:
                     return
                 yield payload, None
 
+    @_retry
     async def reset(self, user_id: str = "default") -> None:
         r = await self._client.post(
             f"{self._url}/reset",
@@ -71,6 +88,7 @@ class HTTPAPIClient:
         )
         r.raise_for_status()
 
+    @_retry
     async def ingest(self, file_path: str) -> dict:
         with open(file_path, "rb") as f:
             filename = os.path.basename(file_path)
@@ -82,16 +100,19 @@ class HTTPAPIClient:
         r.raise_for_status()
         return r.json()
 
+    @_retry
     async def list_documents(self) -> list[str]:
         r = await self._client.get(f"{self._url}/documents", timeout=30)
         r.raise_for_status()
         return r.json().get("documents", [])
 
+    @_retry
     async def delete_document(self, source: str) -> None:
         encoded = urllib.parse.quote(source, safe="")
         r = await self._client.delete(f"{self._url}/documents/{encoded}", timeout=30)
         r.raise_for_status()
 
+    @_retry
     async def save_feedback(
         self,
         user_id: str,