Add modular app structure for L1 server refactoring

Phase 2 of the full modernization:
- App factory pattern with create_app()
- Settings via dataclass with env vars
- Dependency injection container
- Router stubs for auth, storage, api, recipes, cache, runs
- Service layer stubs for run, recipe, cache
- Repository layer placeholder

Routes are stubs that import from legacy server.py during migration.
Next: Migrate each router fully with templates.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app/routers/auth.py

@@ -0,0 +1,119 @@
+"""
+Authentication routes for L1 server.
+
+L1 doesn't handle login directly - users log in at their L2 server.
+Token is passed via URL from L2 redirect, then L1 sets its own cookie.
+"""
+
+from fastapi import APIRouter, Depends, HTTPException, Request
+from fastapi.responses import RedirectResponse
+from fastapi.security import HTTPBearer, HTTPAuthorizationCredentials
+from pydantic import BaseModel
+
+# Import auth utilities from existing server module
+# TODO: Move these to a service
+import sys
+import os
+sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.dirname(os.path.abspath(__file__)))))
+
+router = APIRouter()
+security = HTTPBearer(auto_error=False)
+
+
+class RevokeUserRequest(BaseModel):
+    """Request to revoke all tokens for a user."""
+    username: str
+    l2_server: str
+
+
+@router.get("")
+async def auth_callback(auth_token: str = None):
+    """
+    Receive auth token from L2 redirect and set local cookie.
+
+    This enables cross-subdomain auth on iOS Safari which blocks shared cookies.
+    L2 redirects here with ?auth_token=... after user logs in.
+    """
+    # Import here to avoid circular imports
+    from server import get_verified_user_context, register_user_token
+
+    if not auth_token:
+        return RedirectResponse(url="/", status_code=302)
+
+    # Verify the token is valid
+    ctx = await get_verified_user_context(auth_token)
+    if not ctx:
+        return RedirectResponse(url="/", status_code=302)
+
+    # Register token for this user (for revocation by username later)
+    register_user_token(ctx.username, auth_token)
+
+    # Set local first-party cookie and redirect to runs
+    response = RedirectResponse(url="/runs", status_code=302)
+    response.set_cookie(
+        key="auth_token",
+        value=auth_token,
+        httponly=True,
+        max_age=60 * 60 * 24 * 30,  # 30 days
+        samesite="lax",
+        secure=True
+    )
+    return response
+
+
+@router.get("/logout")
+async def logout():
+    """
+    Logout - clear local cookie and redirect to home.
+
+    Note: This only logs out of L1. User should also logout from L2.
+    """
+    response = RedirectResponse(url="/", status_code=302)
+    response.delete_cookie("auth_token")
+    return response
+
+
+@router.post("/revoke")
+async def revoke_token(
+    credentials: HTTPAuthorizationCredentials = Depends(security),
+):
+    """
+    Revoke a token. Called by L2 when user logs out.
+
+    The token to revoke is passed in the Authorization header.
+    """
+    from server import get_user_context_from_token, revoke_token as do_revoke_token
+
+    if not credentials:
+        raise HTTPException(401, "No token provided")
+
+    token = credentials.credentials
+
+    # Verify token is valid before revoking (ensures caller has the token)
+    ctx = get_user_context_from_token(token)
+    if not ctx:
+        raise HTTPException(401, "Invalid token")
+
+    # Revoke the token
+    newly_revoked = do_revoke_token(token)
+
+    return {"revoked": True, "newly_revoked": newly_revoked}
+
+
+@router.post("/revoke-user")
+async def revoke_user_tokens(request: RevokeUserRequest):
+    """
+    Revoke all tokens for a user. Called by L2 when user logs out.
+
+    This handles the case where L2 issued scoped tokens that differ from L2's own token.
+    """
+    from server import revoke_all_user_tokens
+
+    # Revoke all tokens registered for this user
+    count = revoke_all_user_tokens(request.username)
+
+    return {
+        "revoked": True,
+        "tokens_revoked": count,
+        "username": request.username
+    }