Add Claude provider, OpenRouter fallback, and GFM markdown support

- Add Claude (Anthropic) as third LLM provider with streaming support
- Add OpenRouter as transparent fallback when official API keys are missing or fail
- Add remark-gfm to ReactMarkdown for table/strikethrough rendering
- Claude models: sonnet-4.5, opus-4, opus-4.5, opus-4.6
- Backend: new stream_claude(), stream_openrouter(), provider routing, API key CRUD
- Frontend: model selectors, API key inputs for Claude and OpenRouter
- Auto-migration for new DB columns (claude_api_key, openrouter_api_key)

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

2 files changed, 24 insertions, 2 deletions

diff --git a/backend/app/auth/models.py b/backend/app/auth/models.py
index 8477ba2..14f5bb3 100644
--- a/backend/app/auth/models.py
+++ b/backend/app/auth/models.py
@@ -1,5 +1,5 @@
 import os
-from sqlalchemy import Column, Integer, String, DateTime, Text, create_engine
+from sqlalchemy import Column, Integer, String, DateTime, Text, create_engine, text
 from sqlalchemy.ext.declarative import declarative_base
 from sqlalchemy.orm import sessionmaker
 from datetime import datetime
@@ -26,12 +26,22 @@ class User(Base):
     # API Keys (stored encrypted in production, plain for simplicity here)
     openai_api_key = Column(Text, nullable=True)
     gemini_api_key = Column(Text, nullable=True)
+    claude_api_key = Column(Text, nullable=True)
+    openrouter_api_key = Column(Text, nullable=True)
 
 
 def init_db():
     """Initialize database tables"""
     os.makedirs(DATA_ROOT, exist_ok=True)
     Base.metadata.create_all(bind=engine)
+    # Migrate: add columns that may be missing in existing SQLite databases
+    with engine.connect() as conn:
+        for col in ("claude_api_key", "openrouter_api_key"):
+            try:
+                conn.execute(text(f"ALTER TABLE users ADD COLUMN {col} TEXT"))
+                conn.commit()
+            except Exception:
+                pass  # Column already exists
 
 
 def get_db():
diff --git a/backend/app/auth/routes.py b/backend/app/auth/routes.py
index 3c906b5..eaf897e 100644
--- a/backend/app/auth/routes.py
+++ b/backend/app/auth/routes.py
@@ -228,14 +228,20 @@ async def get_api_keys(current_user: User = Depends(get_current_user)):
     return {
         "openai_api_key": mask_key(current_user.openai_api_key),
         "gemini_api_key": mask_key(current_user.gemini_api_key),
+        "claude_api_key": mask_key(current_user.claude_api_key),
+        "openrouter_api_key": mask_key(current_user.openrouter_api_key),
         "has_openai_key": bool(current_user.openai_api_key),
         "has_gemini_key": bool(current_user.gemini_api_key),
+        "has_claude_key": bool(current_user.claude_api_key),
+        "has_openrouter_key": bool(current_user.openrouter_api_key),
     }
 
 
 class ApiKeysUpdate(BaseModel):
     openai_api_key: Optional[str] = None
     gemini_api_key: Optional[str] = None
+    claude_api_key: Optional[str] = None
+    openrouter_api_key: Optional[str] = None
 
 
 @router.post("/api-keys")
@@ -253,7 +259,13 @@ async def update_api_keys(
     
     if keys.gemini_api_key is not None:
         current_user.gemini_api_key = keys.gemini_api_key if keys.gemini_api_key else None
-    
+
+    if keys.claude_api_key is not None:
+        current_user.claude_api_key = keys.claude_api_key if keys.claude_api_key else None
+
+    if keys.openrouter_api_key is not None:
+        current_user.openrouter_api_key = keys.openrouter_api_key if keys.openrouter_api_key else None
+
     db.commit()
     
     return {"message": "API keys updated successfully"}